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An integrated circuit package includes a processing core for operating on a set of instructions to carry out predefined processes. A plurality of comparators perform compare operations within the integrated circuit package. At least one control register is associated with each of the plurality of comparators, and each of the plurality of comparators are software programmable to control a hysteresis of the comparators responsive to control bits established in the at least one control register of the comparator by the processing core. An amount of positive hysteresis is programmed via a first group of the control bits and an amount of negative hysteresis is programmed via a second group of the control bits.
1. An integrated circuit package on a single chip, comprising:
a processing core for operating on a set of instructions to carry out predefined processes;
a plurality of comparators for performing compare operations within the integrated circuit package;
at least one control register associated with each of the plurality of comparators for storing a first group of control bits controlling an amount of positive hysteresis of each of the plurality of comparators and a second group of control bits controlling an amount of negative hysteresis of each of the plurality of comparators;
wherein each of the plurality of comparators are software programmable to control a hysteresis of the plurality of comparators responsive to control bits established in the at least one control register by the processing core, the amount of positive hysteresis programmed via the first group of the control bits in the at least one control register and the amount of negative hysteresis programmed via the second group of the control bits in the at least one control register;
a crossbar switch for assigning an output of the plurality of comparators to package pins; and
wherein when a comparator output is assigned to the package pins, the comparator output can be programmed by the processing core to operate in either an open drain mode or a push-pull mode.
2. The integrated circuit package of
3. The integrated circuit package of
4. The integrated circuit package of
5. The integrated circuit package of
6. The integrated circuit package of
7. An integrated circuit package, comprising:
a processing core for operating on a set of instructions to carry out predefined processes;
a plurality of comparators for performing compare operations within the integrated circuit package;
at least one control register associated with each of the plurality of comparators for storing a first group of control bits controlling an amount of positive hysteresis of each of the plurality of comparators and a second group of control bits controlling an amount of negative hysteresis of each of the plurality of comparators; and
wherein each of the plurality of comparators are software programmable to control a hysteresis of the plurality of comparators responsive to control bits established in the at least one control register of the comparator by the processing core, the amount of positive hysteresis programmed via the first group of the control bits in the at least one control register and the amount of negative hysteresis programmed via the second group of the control bits in the at least one control register;
wherein each of the plurality of comparators may be software programmed to generate an interrupt on a rising clock edge responsive to a first control bit, a falling clock responsive to a second control bit, and both a rising and falling clock edge responsive to the first and the second control bits; and
wherein each of the plurality of comparators can be enabled or disabled by the processing core responsive to a software programmed bit in the control register.
8. The integrated circuit package of
a crossbar switch for assigning an output of the plurality of comparators to package pins; and
wherein when a comparator output is assigned to the package pins, the comparator output can be programmed by the processing core to operate in either an open drain mode or a push-pull mode.
9. The integrated circuit package of
10. The integrated circuit package of
11. An integrated circuit package on a single chip, comprising:
a processing core for operating on a set of instructions to carry out predefined processes;
a plurality of comparators for performing compare operations within the integrated circuit package;
at least one control register associated with each of the plurality of comparators for storing a first group of control bits controlling an amount of positive hysteresis of each of the plurality of comparators and a second group of control bits controlling an amount of negative hysteresis of comparators;
wherein each of the plurality of comparators are software programmable to control an amount of hysteresis voltage of each of the plurality of comparators and to control a positive going and negative going symmetry of hysteresis around the amount of hysteresis voltage;
a crossbar switch for assigning an output of the plurality of comparators to package pins; and
wherein when a comparator output is assigned to the package pins, the comparator output can be programmed by the processing core to operate in either an open drain mode or a push-pull mode.
This application is a Continuation of U.S. patent application Ser. No.: 11/618,644, filed Dec. 29, 2006, entitled "ANALOG-TO-DIGITAL CONVERTER WITH LOW POWER TRACK-AND-HOLD MODE", which is a Continuation of U.S. Pat. No. 7,171,542, issued on Jan. 30, 2007 and entitled "FIELD PROGRAMMABLE MIXED-SIGNAL CIRCUIT", which claims benefit of Provisional Application No. 60/212,653, filed Jun. 19, 2000, entitled "FIELD PROGRAMMABLE MIXED-SIGNAL CIRCUIT" and is related to U.S. patent application Ser. No. 11/381,707, filed May 4, 2006, entitled "FIELD PROGRAMMABLE MIXED-SIGNAL CIRCUIT", all of which are incorporated herein by reference.
The invention pertains in general to programming integrated circuits and, more particularly to programming integrated circuits via a JTAG interface.
As integrated circuits have seen increased use in recent years, the integration of multiple functions onto a single chip has also increased. Although purely digital circuits require a common technology with respect to transistors, i.e., all CMOS transistors, analog circuitry requires a different technology for such devices as bipolar devices. Each technology facilitates itself to a common processing technology for common devices when only that technology is involved and required. However, whenever audio systems are combined with digital systems, analog technology must be merged with digital technology. This can create problems due to the fact that analog circuitry is sometimes incompatible with the digital clocking signals, especially with respect to analog-to-digital converters. Very high resolution analog-to-digital converters or digital-to-analog converters can be affected by noise created in the digital circuitry. When merging the two technologies together, this is referred to as "mixed-signal" technology.
In current mixed-signal technology, it is desirable to combine the functionality of a microprocessor or microcontroller with an interface to the analog domain through an analog-to-digital converter or a digital-to-analog converter. Further, for many applications, there is a desire for configurability to allow various functions to be emulated or realized with the circuit. Some instrumentation applications require such. The application could be achieved with multiple integrated circuits configured in many different ways, but the desire is for a single chip solution.
The present invention, as disclosed and described herein, in one aspect thereof, comprises an integrated circuit package including a processing core for operating on a set of instructions to carry out predefined processes. A plurality of comparators perform compare operations within the integrated circuit package. Each of the plurality of comparators has associated therewith at least one control register. The plurality of comparators are programmable to operate in a plurality of operating modes responsive to control bits established in the at least one control register of the comparator by the processing core.
For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in conjunction with the accompanying Drawings in which:
The integrated circuit is a fully integrated mixed-signal System on a Chip with a true 12-bit multi-channel ADC 10 with a programmable gain pre-amplifier 12, two 12-bit DACs 14 and 16, two voltage comparators 18 and 20, a voltage reference 22, and an 8051-compatible microcontroller core 24 with 32 kbytes of FLASH memory 26. There are also 12C/SMBUS 28, UART 30, and SPI 32 serial interfaces implemented in hardware (not "bit-banged" in user software) as well as a Programmable Counter/Timer Array (PCA) 34 with five capture/compare modules. There are also 32 general purpose digital Port I/O.
With an on-board VDD monitor 36, WDT, and clock oscillator 37, the integrated circuit is a stand-alone System on a Chip. The MCU effectively configures and manages the analog and digital peripherals. The FLASH memory 26 can be reprogrammed even in-circuit, providing non-volatile data storage, and also allowing field upgrades of the 8051 firmware. The MCU can also individually shut down any or all of the peripherals to conserve power.
A JTAG interface 38 allows the user to interface with the IC. On-board JTAG emulation support allows non-intrusive (uses no on-chip resources), full speed, in-circuit emulation using the production integrated circuit installed in the final application. This emulation system supports inspection and modification of memory and registers, setting breakpoints, watchpoints, single stepping, run and halt commands. All analog and digital peripherals are fully functional when emulating using JTAG.
CIP-51™ Microcontroller Core
The integrated circuit utilizes a microcontroller core 40. The microcontroller 40 is fully compatible with the MCS-51™ instruction set. Standard 803x/805x assemblers and compilers can be used to develop software. The core has all the peripherals included with a standard 8052, including three 16-bit counter/timers, a full-duplex UART, 256 bytes of internal RAM, 128 byte Special Function Register (SFR) address space, and four byte-wide I/O Ports.
The Microcontroller 40 employs a pipelined architecture that greatly increases its instruction throughput over the standard 8051 architecture. In a standard 8051, all instructions except for MUL and DIV take 12 or 24 system clock cycles to execute with a maximum system clock of 12 MHz. By contrast, the Microcontroller 40 core executes seventy percent (70%) of its instructions in one or two system clock cycles, with only four instructions taking more than four system clock cycles. The Microcontroller 40 has a total of 109 instructions. The number of instructions versus the system clock cycles to execute them is as follows:
With the Microcontroller 40's maximum system clock at 20 MHz, it has a peak throughput of 20 MIPS.
Referring now to
An extended interrupt handler 100 provides 22 interrupt sources into the Microcontroller 40 (as opposed to 7 for the standard 8051), allowing the numerous analog and digital peripherals to interrupt the controller. An interrupt driven system requires less intervention by the MCU, giving it more effective throughput. The extra interrupt sources are very useful when building multi-tasking, real-time systems.
There are up to seven reset sources for the system the on-board VDD monitor 36, a Watchdog Timer (WDT), a missing clock detector 104, a voltage level detection from a Comparator 108, a forced software reset on line 114, and two external reset pins 109. The /RST pin 54 is bi-directional, accommodating an external reset, or allowing the internally generated reset to be output on the /RST pin 54. Each reset source except for the VDD monitor and Reset Input Pin may be disabled by the user in software. The WDT 102 may be permanently enabled in software after a power-on reset during MCU initialization. All of the sources are wired Ored with OR circuit 120 to provide a system reset on input 122 to microcontroller 40.
The system has an internal, stand alone clock generator 112 which is used by default as the system clock after any reset. If desired, the clock source may be switched on the fly to the external oscillator 37, which can use a crystal, ceramic resonator, capacitor, RC, or external clock source to generate the system clock. This can be extremely useful in low power applications, allowing the system to run from a slow (power saving) external crystal source, while periodically switching to the fast (up to 15 MHz) internal oscillator as needed.
The Microcontroller 40 has a standard 8051 program and data address configuration. It includes 256 bytes of data RAM, with the upper 128 bytes dual-mapped. Indirect addressing accesses the upper 128 bytes of general purpose RAM, and direct addressing accesses the 128 byte SFR address space. The lower 128 bytes of RAM are accessible via direct and indirect addressing. The first 32 bytes are addressable as four banks of general purpose registers, and the next 16 bytes can be byte addressable or bit addressable.
The integrated circuit program memory consists of 32 k+128 bytes of FLASH in memory 26. This memory 26 may be reprogrammed in-system in 512 byte sectors, and requires no special off-chip programming voltage. The 512 bytes from addresses 0x7E00 to 0x7FFF are reserved for factory use. There is also a single 128-byte sector at address 0x8000 to 0x807F, which may be useful as a small table for software constants or as additional program space. See
JTAG Emulation and Boundary Scan
Referring now to
An emulation system is provided that supports inspection and modification of memory and registers, breakpoints, watchpoints, a stack monitor, and single stepping. No additional target RAM, program memory, timers, or communications channels are required. All the digital and analog peripherals are functional and work correctly while emulating. All the peripherals (except for the ADC) are stalled when the MCU is halted, during single stepping, or at a breakpoint in order to keep them in sync.
A development software application 202 is provided with an emulation cartridge 200 to develop application code and perform in-circuit emulation with the integrated circuit. The software includes a developer's studio and debugger, and an integrated 8051 assembler. A target application board 204 is provided with a integrated circuit installed and large prototyping area, plus an RS-232 cable 208 and JTAG cable 210, and wall-mount power supply. The Development Kit requires a Windows 95/98 or NT computer with one available RS-232 serial port. A PC 214 is connected via the RS-232 cable 208 to the Emulation Cartridge 200. A six-inch ribbon cable connects the Emulation Cartridge 200 to the target application board 204, picking up the four JTAG pins and VDD and GND. The Emulation Cartridge 200 takes its power from the application board. It requires roughly 20 mA at 2.7-3.6V. For applications where there is not sufficient power available from the target application board 204, the provided power supply can be connected directly to the Emulation Cartridge 200.
Programmable Digital I/O and Crossbar
Referring now to
The on-board counter/timers, serial buses, HW interrupts, ADC Start of Conversion input, comparator outputs, and other digital signals in the digital crossbar switch 52 can be configured to appear on the Port I/O pins 300 specified in Crossbar Control registers 402. This allows the user to select the exact mix of general purpose Port I/O and digital resources needed for his particular application.
The digital cross-bar switch 52 has a priority decoder 404 that is associated therewith. The lowest priority group that can be interfaced with are the SMBUS 28, SPI 32, UART 30, PCA 34, the T0, T1 and T2 block 406 and general miscellaneous computer outputs 410. Additionally, there are the port latches which are interfaced through lines 412 to the cross-bar 52.
The I/O side is interfaced to BUSes 414, 416 and 418, respectively, all networked for each of the cell 420 interfaces with eight external pins, such that there are three banks of pins. They range from the highest priority at Port 0 associated with the cell one 420 to the lowest priority associated with the cell 424. There is also provided a fourth port cell 426, associated with a second set of eight outputs. These are directly interfaced to the port latches. The detailed description of digital cross-bar switch 52 is described in U.S. patent application Ser. No. 09/583,260, filed May 31, 2000, entitled CROSS-BAR MATRIX FOR CONNECTING DIGITAL RESOURCES TO I/O PINS OF AN INTEGRATED CIRCUIT, which is incorporated herein by reference.
Programmable Counter Array
Referring now to
Each capture/compare module 502-510 can be configured to operate in one of four modes: Edge-Triggered Capture, Software Timer, High Speed Output, or Pulse Width Modulator. The PCA Capture/Compare Module I/O and External Clock Input are routed to the integrated circuit Port I/O via the Digital Crossbar.
Serial Ports
The integrated circuit, as described hereinabove, includes a Full-Duplex UART, SPI BUS, and I2C/SMBUS. Each of the serial buses is fully implemented in hardware and makes extensive use of the Microcontroller 40's interrupts, thus requiring very little intervention by the CPU. The serial buses do not "share" resources such as timers, interrupts, or Port I/O, so any or all of the ports may be used together or separately with any other.
Analog to Digital Converter
Referring now to
The ADC 10 is under full control of the Microcontroller 40 via the Special Function Registers. One input channel is tied to an internal temperature sensor 552, while the other eight channels are available externally through pins 556. Each pair of the eight external input channels can be configured as either two single-ended inputs or a single differential input. The system controller can also put the ADC 10 into shutdown to save power.
The programmable gain amplifier 12 follows the analog multiplexer 550. The gain can be set in software from 0.5 to 16 in powers of 2. The gain stage can be especially useful when different ADC input channels have widely varied input voltage signals, or when it is necessary to "zoom in" on a signal with a large DC offset (in differential mode, a DAC could be used to provide the DC offset).
Conversions can be started in four ways; a software command, an overflow on Timer 2, an overflow on Timer 3, or an external signal input. This flexibility allows the start of conversion to be triggered by software events, external HW signals, or convert continuously. A completed conversion causes an interrupt, or a status bit can be polled in software to determine the end of conversion. The resulting 12-bit data word is latched into two SFRs upon completion of a conversion. The data can be right or left justified in these registers under software control.
Compare registers for the ADC data can be configured to interrupt the controller when ADC data is within a specified window. The ADC can monitor a key voltage continuously in background mode, but not interrupt the controller unless the converted data is within the specified window. The ADC is described in U.S. patent application Ser. No. 09/595,959, filed Jun. 19, 2000, and entitled DIFFERENTIAL/SINGLE ENDED ANALOG-TO-DIGITAL CONVERTER, and in U.S. patent application Ser. No. 09/638,095, filed Aug. 11, 2000, entitled PROGRAMMABLE GAIN ADC, and in U.S. patent application Ser. No. 09/637,493, filed Aug. 11, 2000, and entitled COMPARATOR-AMPLIFIER CONFIGURATION IN AN ADC, and in U.S. patent Ser. No. 09/419,148, filed Oct. 15, 1999, and entitled A/D CONVERTER WITH VOLTAGE/CHARGE SCALING, all of which are incorporated herein by reference.
Comparators and DACs
Referring now to
The DACs are voltage output mode and use the same voltage reference as the ADC 10. They are especially useful as references for the comparators or offsets for the differential inputs of the ADC 10. The operation of the DACs 14 and 16 is described in U.S. patent application Ser. No. 09/583,341, filed May 31, 2000, and entitled SEGMENTED D/A CONVERTER WITH ENHANCED DYNAMIC RANGE, and in U.S. patent application Ser. No. 09/584,311, filed May 31, 2000, and entitled D/A CONVERTER STREET EFFECT COMPENSATION, all of which are incorporated herein by reference.
Pinout and Package Definitions
The following are the pin definitions for various configurations.
Referring now to
Analog Multiplexer and PGA
Eight of the AMUX channels are available for external measurements while the ninth channel is internally connected to an on-board temperature sensor 552 (temperature transfer function is shown in
ADC Modes of Operation
The ADC has a maximum conversion speed of 100 ksps. The ADC conversion clock is derived from the system clock. Conversion speed can be reduced by a factor of 2, 4, 8 or 16 via the ADCSC bits in the ADC0CF Register 616. This is useful to adjust conversion speed to accommodate different system clock speeds.
A conversion can be initiated in one of four ways, depending on the programmed states of the ADC Start of Conversion Mode bits (ADSTM1, ADSTM0) in an ADC0CN register 618. Conversions may be initiated by:
Writing a 1 to ADBUSY provides software control of the ADC whereby conversions are performed "on-demand". During conversion, the ADBUSY bit is set to 1 and restored to 0 when conversion is complete. The falling edge of ADBUSY triggers an interrupt (when enabled) and sets the interrupt flag in ADC0CN. Converted data is available in the ADC data word MSB and LSB registers, ADC0H, ADC0L. Converted data can be either left or right justified in the ADC0H:ADC0L register pair depending on the programmed state of the ADLJST bit in the ADC0CN register. This is illustrated in Table 5.
The ADCTM bit in register ADC0CN 618 controls the ADC track-and-hold mode. In its default state, the ADC input is continuously tracked, except when a conversion is in progress. Setting ADCTM to 1 allows one of four different low power track-and-hold modes to be specified by states of the ADSTM1-0 bits (also in ADC0CN):
Modes 1, 2 and 3 (above) are useful when the start of conversion is triggered in software command or when the ADC is operated continuously. Mode 4 is used when the start of conversion is triggered by external hardware. In this case, the track-and-hold is in its low power mode at times when the CNVSTR input is high. Tracking can also be disabled (shutdown) when the entire chip is in low power standby or sleep modes.
ADC Programmable Window Detector
The ADC programmable window detector is very useful in many applications. It continuously compares the ADC output to user-programmed limits and notifies the system when an out-of-band condition is detected. This is especially effective in an interrupt-driven system, saving code space and CPU bandwidth while delivering faster system response times. The window detector interrupt flag (ADWINT in ADC0CN) can also be used in polled mode. The high and low bytes of the reference words are loaded into the ADC Greater-Than and ADC Less-Than registers (ADC0GTH, ADC0GTL, ADC0LTH, and ADC0LTL).
DACs 12 Bit Voltage Mode
Referring now to
The DAC0 enable/disable function is controlled by the DAC0EN bit (DAC0CN.7). Writing a 1 to DAC0EN enables DAC0 while writing a 0 to DAC0EN disables DAC0 with switch 656. While disabled, the output of DAC0 is maintained in a high-impedance state, and the DAC0 supply current falls to 1 uA or less.
In some instances, input data should be shifted prior to a DAC0 write operation to properly justify data within the DAC input registers. This action would typically require one or more load and shift operations, adding software overhead and slowing DAC throughput. To alleviate this problem, the data-formatting feature provides a means for the user to program the orientation of the DAC0 data word within data registers DAC0H and DAC0L. The three DAC0DF bits (DAC0CN.[2:0]) allow the user to specify one of five data word orientations as shown in the DAC0CN register definition. DAC1 is functionally the same as DAC0 described above. DAC1 is functionally the same as DAC0 described above in Tables 8-13.
Referring now to
The hysteresis of each comparator is software-programmable via its respective Comparator control register (CPT0CN 660, CPT1CN 662). The user can program both the amount of hysteresis voltage (referred to the input voltage) and the positive and negative-going symmetry of this hysteresis around the threshold voltage. The output of the comparator can be polled in software, or can be used as an interrupt source. Each comparator can be individually enabled or disabled (shutdown). When disabled, the comparator output (if assigned to a Port I/O pin via the Crossbar) defaults to the logic low state, its interrupt capability is suspended and its supply current falls to less than 1 uA. Comparator 0 inputs can be externally driven from −0.25V to (AV+)+0.25V without damage or upset.
The Comparator 0 hysteresis is programmed using bits 3-0 in the Comparator 0 Control Register CPT0CN (shown in Table 11). The amount of negative hysteresis voltage is determined by the settings of the CP0HYN bits. As shown in
Comparator interrupts can be generated on both rising-edge and falling-edge output transitions. The CP0FIF flag is set upon a Comparator 0 falling-edge interrupt, and the CP0RIF flag is set upon the Comparator 0 rising-edge interrupt. Once set, these bits remain set until cleared by the CPU. The Output State of Comparator 0 can be obtained at any time by reading the CP0OUT bit. Comparator 0 is enabled by setting the CP0EN bit, and is disabled by clearing this bit. Comparator 0 can also be programmed as a reset source.
The operation of Comparator 1 is identical to that of Comparator 0, except the Comparator 1 is controlled by the CPT1CN Register as set forth in Table 12. Also, Comparator 1 can not be programmed as a reset source.
Voltage Reference
Referring now to
If a different reference voltage is required, an external reference 674 can be connected to the VREF pin and the internal bandgap and buffer amplifier disabled in software. The external reference voltage must still be less than AV+−0.3V. A Reference Control Register 676, REF0CN (defined in Table 13), provides for enabling or disabling the bandgap and buffer amplifier 670. The BIASE bit in REF0CN enables the on-board bandgap reference while the REFBE bit enables the buffer amplifier 670 which drives the VREF pin. When disabled, the supply current drawn by the bandgap and buffer amplifier falls to less than 1 uA (typical) and the output of the buffer amplifier 670 enters a high impedance state. If the internal bandgap is used as the reference voltage generator, BIASE and REFBE must both be set to 1. If an external reference 674 is used, REFBE must be set to 0 and BIASE must be set to 1. If neither the ADC nor the DAC are being used, both of these bits can be set to 0 to conserve power.
The temperature sensor connects to the highest order input of the A/D converter's input multiplexer. The TEMPE bit within REF0CN enables and disables the temperature sensor. While disabled, the temperature sensor defaults to a high impedance state and any A/D measurements performed on the sensor while disabled result in meaningless data.
Referring now to
The Microcontroller 40 core implements the standard 8051 organization and peripherals as well as additional custom peripherals and functions to extend its capability. The Microcontroller 40 includes the following features:
The Microcontroller 40 employs a pipelined architecture that greatly increases its instruction throughput over the standard 8051 architecture. In a standard 8051, all instructions except for MUL and DIV take 12 or 24 system clock cycles to execute, and usually have a maximum system clock of 12 MHz. By contrast, the Microcontroller 40 core executes seventy percent (70%) of its instructions in one or two system clock cycles, with no instructions taking more than eight system clock cycles.
With the Microcontroller 40's maximum system clock at 20 MHz, it has a peak throughput of 20 MIPS. The Microcontroller 40 has a total of 109 instructions. The number of instructions versus the system clock cycles required to execute them is as follows:
A JTAG-based serial interface is provided for in-system programming of the Flash program memory and communication with on-chip emulation support logic. The reprogrammable Flash can also be read and changed a single byte at a time by the application software using the MOVC and MOVX instructions. This feature allows program memory to be used for non-volatile data storage as well as updating program code under software control.
The on-chip emulation support logic facilitates full speed in-circuit debugging, allowing the setting of hardware breakpoints and watch points, starting, stopping and single stepping through program execution (including interrupt service routines), examination of the program's call stack, and reading/writing the contents of registers and memory. This method of on-chip emulation is completely non-intrusive and non-evasive, requiring no RAM, Stack, timers, or other on-chip resources.
Instruction Set
The instruction set of the Microcontroller 40 System Controller is fully compatible with the standard MCS-51™ instruction set. Standard 8051 development tools can be used to develop software for the Microcontroller 40. All Microcontroller 40 instructions are the binary and functional equivalent of their MCS-51™ counterparts, including opcodes, addressing modes and effect on PSW flags. However, instruction timing is different than that of the standard 8051.
Instruction and CPU Timing
In many 8051 implementations, a distinction is made between machine cycles and clock cycles, with machine cycles varying from 2 to 12 clock cycles in length. However, the Microcontroller 40 implementation is based solely on clock cycle timing. All instruction timings are specified in terms of clock cycles.
Due to the pipelined architecture of the Microcontroller 40, most instructions execute in the same number of clock cycles as there are program bytes in the instruction. Conditional branch instructions take one less clock cycle to complete when the branch is not taken as opposed to when the branch is taken. Table 14 illustrates the Instruction Set Summary for the Microcontroller 40, which includes the mnemonic, number of bytes, and number of clock cycles for each instruction.
MOVX Instruction and Program Memory
The MOVX instruction is typically used to access external data memory. The Microcontroller 40 does not support external data or program memory. In the Microcontroller 40, the MOVX instruction accesses the on-chip program memory space implemented as re-programmable Flash memory. This feature provides a mechanism for the Microcontroller 40 to update program code and use the program memory space for non-volatile data storage.
Referring now to
Program Memory
The Microcontroller 40 has a 64K-byte program memory space. The MCU implements 32896 bytes of this program memory space as in-system, reprogrammable Flash memory, organized in a contiguous block from addresses 0x0000 to 0x807F. Note: 512 bytes (0x7E00-0x7FFF) of this memory are reserved for factory use and are not available for user program storage.
Program memory is normally assumed to be read-only. However, the Microcontroller 40 can write to program memory by setting the Program Store Write Enable bit (PSCTL.7) and using the MOVX instruction. This feature provides a mechanism for the Microcontroller 40 to update program code and use the program memory space for non-volatile data storage.
Data Memory
The Microcontroller 40 implements 256 bytes of internal RAM mapped into the data memory space from 0x00 through 0xFF. The lower 128 bytes of data memory are used for general purpose registers and scratch pad memory. Either direct or indirect addressing may be used to access the lower 128 bytes of data memory. Locations 0x00 through 0x1F are addressable as four banks of general purpose registers 694, each bank consisting of eight byte-wide registers. The next 16 bytes, locations 0x20 through 0x2F, may either be addressed as bytes or as 128 bit locations accessible with the direct addressing mode.
The upper 128 bytes of data memory are accessible only by indirect addressing. This region occupies the same address space as the Special Function Registers (SFR) but is physically separate from the SFR space. The addressing mode used by an instruction when accessing locations above 0x7F determines whether the CPU accesses the upper 128 bytes of data memory space or the SFRs. Instructions that use direct addressing will access the SFR space. Instructions using indirect addressing above 0x7F access the upper 128 bytes of data memory.
General Purpose Registers
The lower 32 bytes of data memory, locations 0x00 through 0x1F, may be addressed as four banks of general-purpose registers. Each bank consists of eight byte-wide registers designated R0 through R7. Only one of these banks may be enabled at a time. Two bits in the program status word, RS0 (PSW.3) and RS1 (PSW.4), select the active register bank (see description of the PSW in Table 15). This allows fast context switching when entering subroutines and interrupt service routines. Indirect addressing modes use registers R0 and R1 as index registers.
Bit Addressable Locations
In addition to direct access to data memory organized as bytes, the sixteen data memory locations at 0x20 through 0x2F are also accessible as 128 individually addressable bits. Each bit has a bit address from 0x00 to 0x7F. Bit 0 of the byte at 0x20 has bit address 0x00 while bit 7 of the byte at 0x20 has bit address 0x07. Bit 7 of the byte at 0x2F has bit address 0x7F. A bit access is distinguished from a full byte access by the type of instruction used (bit source or destination operands as opposed to a byte source or destination).
The MCS-51™ assembly language allows an alternate notation for bit addressing of the form XX.B where XX is the byte address and B is the bit position within the byte. For example, the instruction:
MOV C, 22.3 h
moves the Boolean value at 0x13 (bit 3 of the byte at location 0x22) into the user Carry flag.
A programmer's stack can be located anywhere in the 256-byte data memory. The stack area is designated using the Stack Pointer (SP, 0x81) SFR. The SP will point to the last location used. The next value pushed on the stack is placed at SP+1 and then SP is incremented. A reset initializes the stack pointer to location 0x07. Therefore, the first value pushed on the stack is placed at location 0x08, which is also the first register (R0) of register bank 1. Thus, if more than one register bank is to be used, the SP should be initialized to a location in the data memory not being used for data storage. The stack depth can extend up to 256 bytes.
The MCU also has built-in hardware for a stack record. The stack record is a 32-bit shift register, where each Push or increment SP pushes one record bit onto the register, and each Call pushes two record bits onto the register. (A Pop or decrement SP pops one record bit, and a Return pops two record bits, also.) The stack record circuitry can also detect an overflow or underflow on the 32-bit shift register, and can notify the emulator software even with the MCU running full-speed emulation.
Special Function Registers
The direct-access data memory locations from 0x80 to 0xFF constitute the special function registers (SFRs). The SFRs provide control and data exchange with the Microcontroller 40's resources and peripherals. The Microcontroller 40 duplicates the SFRs found in a typical 8051 implementation as well as implementing additional SFRs used to configure and access the sub-systems unique to the MCU. This allows the addition of new functionality while retaining compatibility with the MCS-51™ instruction set. Table 16 lists the SFRs implemented in the Microcontroller 40 System Controller. Registers unique to the Microcontroller 40 are shown in bold type.
The SFR registers are accessed anytime the direct addressing mode is used to access memory locations from 0x80 to 0xFF. SFRs with addresses ending in 0x0 or 0x8 (e.g. P0, TCON, P1, SCON, IE, etc.) are bit-addressable as well as byte-addressable. All other SFRs are byte-addressable only. Unoccupied addresses in the SFR space are reserved for future use. Accessing these areas will have an indeterminate effect and should be avoided. Table 17 describes the operation of each register.
In Tables 16-20 are descriptions of SFRs related to the operation of the Microcontroller 40 System Controllers Reserved bits should not be set to logic 1. The system may use these bits to implement additional features in which case the reset value of the bit will be logic 0, selecting the feature's default states Detailed descriptions of the remaining SFRs are included hereinbelow.
Interrupt Handler
The Microcontroller 40 includes an extended interrupt system supporting a total of 22 interrupt sources with two priority levels. The allocation of interrupt sources between on-chip peripherals and external inputs pins varies according to the specific version of the devices. Each interrupt source has one or more associated interrupt-pending flag(s) located in an SFR. When a peripheral or external source meets a valid interrupt condition, the associated interrupt-pending flag is set to logic 1.
If interrupts are enabled for the source, an interrupt request is generated when the interrupt-pending flag is set. As soon as execution of the current instruction is complete, the CPU generates an LCALL to a predetermined address to begin execution of an interrupt service routine (ISR). Each ISR must end with an RETI instruction, which returns program execution to the next instruction that would have been executed if the interrupt request had not occurred. If interrupts are not enabled, the interrupt-pending flag is ignored by the hardware and program execution continues as normal. (The interrupt-pending flag is set to logic 1 regardless of the interrupt's enable/disable state.)
Each interrupt source can be individually enabled or disabled through the use of an associated interrupt enable bit in an SFR (IE-EIE2). However, interrupts must first be globally enabled by setting the EA bit (IE.7) to logic 1 before the individual interrupt enables are recognized. Setting the EA bit to logic 0 disables all interrupt sources regardless of the individual interrupt-enable settings.
Some interrupt-pending flags are automatically cleared by the hardware when the CPU vectors to the ISR. However, most are not cleared by the hardware and must be cleared by software before returning from the ISR. If an interrupt-pending flag remains set after the CPU completes the return-from-interrupt (RETI) instruction, a new interrupt request will be generated immediately and the CPU will re-enter the ISR after the completion of the next instruction.
MCU Interrupt Sources and Vectors
The MCU allocates 12 interrupt sources to on-chip peripherals. Up to 10 additional external interrupt sources are available depending on the I/O pin configuration of the device. Software can simulate an interrupt by setting any interrupt-pending flag to logic 1. If interrupts are enabled for the flag, an interrupt request will be generated and the CPU will vector to the ISR address associated with the interrupt-pending flag. Refer to the datasheet section associated with a particular on-chip peripheral for information regarding valid interrupt conditions for the peripheral and the behavior of its interrupt-pending flag(s).
External Interrupts
Two of the external interrupt sources (/INT0 and /INT1) are configurable as active-low level-sensitive or active-low edge-sensitive inputs depending on the setting of IT0 (TCON.0) and IT1 (TCON.2). IE0 (TCON.1) and IE1 (TCON.3) serve as the interrupt-pending flag for the /INT0 and /INT1 external interrupts, respectively. If an /INT0 or /INT1 external interrupt is configured as edge-sensitive, the corresponding interrupt-pending flag is automatically cleared by the hardware when the CPU vectors to the ISR. When configured as level sensitive, the interrupt-pending flag follows the state of the external interrupt's input pin. The external interrupt source must hold the input active until the interrupt request is recognized. It must then deactivate the interrupt request before execution of the ISR completes or another interrupt request will be generated.
The remaining four external interrupts (External Interrupts 4-7) are active-low, edge-sensitive inputs. The interrupt-pending flags for these interrupts are in the Port 1 Interrupt Flag Register shown in Table 21.
Each interrupt source can be individually programmed to one of two priority levels: low or high. A low priority interrupt service routine can be preempted by a high priority interrupt. A high priority interrupt cannot be preempted. Each interrupt has an associated interrupt priority bit in an SFR (IP-EIP2) used to configure its priority level. Low priority is the default. If two interrupts are recognized simultaneously, the interrupt with the higher priority is serviced first. If both interrupts have the same priority level, a fixed priority order is used to arbitrate.
Interrupt Latency
Interrupt response time depends on the state of the CPU when the interrupt occurs. Pending interrupts are sampled and priority decoded each system clock cycle. Therefore, the fastest possible response time is 5 system clock cycles: 1 clock cycle to detect the interrupt and 4 clock cycles to complete the LCALL to the ISR. If an interrupt is pending when a RETI is executed, a single instruction is executed before an LCALL is made to service the pending interrupt. Therefore, the maximum response time for an interrupt (when no other interrupt is currently being serviced or the new interrupt is of greater priority) occurs when the CPU is performing an RETI instruction followed by a DIV as the next instruction. In this case, the response time is 18 system clock cycles: 1 clock cycle to detect the interrupt, 5 clock cycles to execute the RETI, 8 clock cycles to complete the DIV instruction and 4 clock cycles to execute the LCALL to the ISR. If the CPU is executing an ISR for an interrupt with equal or higher priority, the new interrupt will not be serviced until the current ISR completes, including the RETI and following instruction.
Interrupt Register Descriptions
The SFRs used to enable the interrupt sources and set their priority level are described herein in Tables 22-27 below.
Power Management Modes
The Microcontroller 40 core has two software programmable power management modes: Idle and Stop. Idle mode halts the CPU while leaving the external peripherals and internal clocks active. In Stop mode, the CPU is halted, all interrupts and timers (except the Missing Clock Detector) are inactive, and the system clock is stopped. Since clocks are running in Idle mode, power consumption is dependent upon the system clock frequency and the number of peripherals left in active mode before entering Idle. Stop mode consumes the least power. Table 28 describes the Power Control Register (PCON) used to control the Microcontroller 40's power management modes.
Although the Microcontroller 40 has Idle and Stop modes built in (as with any standard 8051 architecture), power management of the entire MCU is better accomplished by enabling/disabling individual peripherals as needed. Each analog peripheral can be disabled when not in use and put into low power mode. Digital peripherals, such as timers or serial buses, draw little power whenever they are not in use. Turning off the Flash memory saves power, similar to entering Idle mode. Turning off the oscillator saves even more power, but requires a reset to restart the MCU.
Idle Mode
Setting the Idle Mode Select bit (PCON.0) causes the Microcontroller 40 to halt the CPU and enter Idle mode as soon as the instruction that sets the bit completes. All internal registers and memory maintain their original data. All analog and digital peripherals can remain active during Idle mode.
Idle mode is terminated when an enabled interrupt or /RST is asserted. The assertion of an enabled interrupt will cause the Idle Mode Selection bit (PCON.0) to be cleared and the CPU will resume operation. The pending interrupt will be serviced and the next instruction to be executed after the return from interrupt (RETI) will be the instruction immediately following the one that set the Idle Mode Select bit. If Idle mode is terminated by an internal or external reset, the Microcontroller 40 performs a normal reset sequence and begins program execution at address 0x0000.
If enabled, the WDT will eventually cause an internal watchdog reset and thereby terminate the Idle mode. This feature protects the system from an unintended permanent shutdown in the event of an inadvertent write to the PCON register. If this behavior is not desired, the WDT may be disabled by software prior to entering the Idle mode if the WDT was initially configured to allow this operation. This provides the opportunity for additional power savings, allowing the system to remain in the Idle mode indefinitely, waiting for an external stimulus to wake up the system.
Stop Mode
Setting the Stop Mode Select bit (PCON.1) (Table 28) causes the Microcontroller 40 to enter Stop mode as soon as the instruction that sets the bit completes. In Stop mode, the CPU and oscillators are stopped, effectively shutting down all digital peripherals. Each analog peripheral must be shut down individually prior to entering Stop Mode. Stop mode can only be terminated by an internal or external reset. On reset, the Microcontroller 40 performs the normal reset sequence and begins program execution at address 0x0000.
If enabled, the Missing Clock Detector will cause an internal reset and thereby terminate the Stop mode. The Missing Clock Detector should be disabled if the CPU is to be put to sleep for longer than the MCD timeout of 100 usec.
Flash Memory
Referring now to
Programming the Flash Memory
The simplest technique of programming the Flash memory is through the JTAG interface using programming tools provided by manufacturer or a third party vendor. This is the only means for programming a non-initialized device. For details on the JTAG commands to program Flash memory.
The Flash memory can be programmed by software using the MOVX instruction with the address and data byte to be programmed provided as normal operands. Before writing to Flash memory using MOVX, write operations must be enabled by setting the PSWE Program Store Write Enable bit (PSCTL.0) to logic 1. Writing to Flash remains enabled until the PSWE bit is cleared by software.
Writes to Flash memory can clear bits but cannot set them. Only an erase operation can set bits in Flash. Therefore, the byte location to be programmed must be erased before a new value can be written. The 32 kbyte Flash memory is organized in 512-byte sectors. The erase operation applies to an entire sector (setting all bytes in the sector to 0xFF). Setting the PSEE Program Store Erase Enable bit (PSCTL.1) to logic 1 and then using the MOVX command to write a data byte to any byte location within the sector will erase an entire 512-byte sector. The data byte written can be of any value because it is not actually written to the Flash. Flash erasure remains enabled until the PSEE bit is cleared by software. The following sequence illustrates the algorithm for programming the Flash memory by software:
Write/Erase timing is automatically controlled by hardware based on the prescaler value held in the Flash Memory Timing Prescaler register (FLSCL). The 4-bit prescaler value FLASCL determines the time interval for write/erase operations. The FLASCL value required for a given system clock is shown in Table 30, along with the formula used to derive the FLASCL values. When FLASCL is set to 1111b, the write/erase operations are disabled. Note that code execution in the 8051 is stalled while the Flash is being programmed or erased.
Non-volatile Data Storage
The Flash memory can be used for non-volatile data storage as well as program code. This allows data such as calibration coefficients to be calculated and stored at run time. Data is written using the MOVX instruction and read using the MOVC instruction.
The MCU incorporates an additional 128-byte sector of Flash memory located at 0x8000−0x807F. This sector can be used for program code or data storage. However, its smaller sector size makes it particularly well suited as general purpose, non-volatile scratchpad memory. Even though Flash memory can be written a single byte at a time, an entire sector must be erased first. In order to change a single byte of a multi-byte data set, the data must be moved to temporary storage. Next, the sector is erased, the data set updated and the data set returned to the original sector. The 128-byte sector-size facilitates updating data without wasting program memory space by allowing the use of internal data RAM for temporary storage. (A normal 512-byte sector is too large to be stored in the 256-byte internal data memory.)
Security Options
The Microcontroller 40 provides security options to protect the Flash memory from inadvertent modification by software as well as prevent the viewing of proprietary program code and constants. The Program Store Write Enable (PSCTL.0) (Table 29) and the Program Store Erase Enable (PSCTL.1) bits protect the Flash memory from accidental modification by software. These bits must be explicitly set to logic 1 before software can modify the Flash memory. Additional security features prevent proprietary program code and data constants from being read or altered across the JTAG interface or by software running on the system controller. Tables 30 and 31 illustrate these features.
A set of security lock bytes stored at 0x7DFE and 0x7DFF protect the Flash program memory from being read or altered across the JTAG interface. Each bit in a security lock-byte protects one 4 kbyte block of memory. Clearing a bit to logic 0 in a Read lock byte prevents the corresponding block of Flash memory from being read across the JTAG interface. Clearing a bit in the Write/Erase lock byte protects the block from JTAG erasures and/or writes. The Read lock byte is at location 0x7DFF. The Write/Erase lock byte is located at 0x7DFE.
The lock bits can always be read and cleared to logic 0 regardless of the security setting applied to the block containing the security bytes. This allows additional blocks to be protected after the block containing the security bytes has been locked. However, the only means of removing a lock once set is to erase the entire program memory space by performing a JTAG erase operation. It is noted that erasing the Flash memory block containing the security bytes will automatically initiate erasure of the entire program memory space (except for the reserved area). This erasure can only be performed via the JTAG.
The Flash Access Limit security feature protects proprietary program code and data from being read by software running on the Microcontroller 40. This feature provides support for OEMs that wish to program the MCU with proprietary value-added firmware before distribution. The value-added firmware can be protected while allowing additional code to be programmed in remaining program memory space later.
The Software Read Limit (SRL) is a 16-bit address that establishes two logical partitions in the program memory space. The first is an upper partition consisting of all the program memory locations at or above the SRL address, and the second is a lower partition consisting of all the program memory locations starting at 0x0000 up to (but excluding) the SRL address. Software in the upper partition can execute code in the lower partition, but is prohibited from reading locations in the lower partition using the MOVC instruction. (Executing a MOVC instruction from the upper partition with a source address in the lower partition will always return a data value of 0x00.) Software running in the lower partition can access locations in both the upper and lower partition without restrictions.
The Value-added firmware should be placed in the lower partition. On reset, control is passed to the value-added firmware via the reset vector. Once the value-added firmware completes its initial execution, it branches to a predetermined location in the upper partition. If entry points are published, software running in the upper partition may execute program code in the lower partition, but it cannot read the contents of the lower partition. Parameters may be passed to the program code running in the lower partition either through the typical method of placing them on the stack or in registers before the call or by placing them in prescribed memory locations in the upper partition.
The SRL address is specified using the contents of the Flash Access Register. The 16-bit SRL address is calculated as 0xNN00, where NN is the contents of the SRL Security Register. Thus, the SRL can be located on 256-byte boundaries anywhere in program memory space. However, the 512-byte erase sector size essentially requires that a 512 boundary be used. The contents of a non-initialized SRL security byte is 0x00, thereby setting the SRL address to 0x0000 and allowing read access to all locations in program memory space by default.
Reset Sources
Referring back to
All of the SFRs are reset to predefined values. The reset values of the SFR bits are defined in the SFR detailed descriptions. The contents of internal data memory are not changed during a reset and any previously stored data is preserved. However, since the stack pointer SFR is reset, the stack is effectively lost even though the data on the stack are not altered.
The I/O port latches are reset to 0xFF (all logic ones), activating internal weak pull-ups which take the external I/O pins to a high state. The external I/O pins do not go high immediately, but will go high within 4 system clock cycles after entering the reset state. If the source of reset is from the VDD Monitor, the /RST pin is driven low until the end of the VDD reset timeout.
On exit from the reset state, the Core 40 uses the internal oscillator running at 1.9 MHz as the system clock by default. The Watchdog Timer 102 is enabled using its longest timeout interval. Once the system clock source is stable, program execution begins at location 0x0000.
There are seven sources for putting the MCU into the reset state: power-on/power-fail, external /RST pin, external CNVSTR signal, software commanded, Comparator 0, Missing Clock Detector, and Watchdog Timer. Each reset source is described below:
Power-on Reset
The Microcontroller 40 incorporates a power supply monitor that holds the MCU in the reset state until VDD rises above the VRST level during power-up. The /RST pin is asserted (low) until the end of the 100 msec VDD Monitor timeout in order to allow the VDD supply to become stable.
On exit from a power-on reset, the PORSF flag (RSTSRC.1) is set by hardware to logic 1. All of the other reset flags in the RSTSRC Register are indeterminate. It is cleared by all other resets. Since all resets cause program execution to begin at the same location (0x0000) software can read the PORSF flag to determine if a power-up was the cause of reset. The content of internal data memory should be assumed to be undefined after a power-on reset.
Software Forced Reset
Writing a 1 to the PORSF bit forces a Power-On Reset.
Power-fail Reset
When a power-down transition or power irregularity causes VDD to drop below VRST, the power supply monitor will drive the /RST pin low and return the Microcontroller 40 to the reset state (see
External Reset
The external /RST pin provides a means for external circuitry to force the Microcontroller 40 into a reset state. Asserting an active-low signal on the /RST pin will cause the Microcontroller 40 to enter the reset state. It may be desirable to provide an external pull-up and/or decoupling of the /RST pin to avoid erroneous noise-induced resets. The Microcontroller 40 will remain in reset until at least 12 clock cycles after the active-low /RST signal is removed. The PINRSF flag (RSTSRC.0) is set on exit from an external reset.
Missing Clock Detector Reset
The Missing Clock Detector is essentially a one-shot circuit that is triggered by the MCU system clock. If the system clock goes away for more than 100 usec, the one-shot will time out and generate a reset. After a Missing Clock Detector reset, the MCDRSF flag (RSTSRC.2) will be set, signifying the MSD as the reset source; otherwise, this bit reads 0. The state of the /RST pin is unaffected by this reset. Setting the MSCLKE bit in the OSCICN register enables the Missing Clock Detector.
Comparator 0 Reset
Comparator 0 can be configured as a reset input by writing a 1 to the C0RSEF flag (RSTSRC.5). Comparator 0 should be enabled using CPT0CN.7 (see Table 11) prior to writing to C0RSEF to prevent any turn-on chatter on the output from generating an unwanted reset. When configured as a reset, if the non-inverting input voltage (on CP0+) is less than the inverting input voltage (on CP0−), the MCU is put into the reset state. After a Comparator 0 Reset, the C0RSEF flag (RSTSRC.5) will read 1 signifying Comparator 0 as the reset source; otherwise, this bit reads 0. The state of the /RST pin is unaffected by this reset.
External CNVSTR Pin Reset
The external CNVSTR signal can be configured as a reset input by writing a 1 to the CNVRSEF flag (RSTSRC.6). The CNVSTR signal can appear on any of the P0, P1, or P2 I/O pins. (Note that the Crossbar 52 must be configured for the CNVSTR signal to be routed to the appropriate Port I/O.) The Crossbar 52 should be configured and enabled before the CNVRSEF is set to configure CNVSTR as a reset source. When configured as a reset, CNVSTR is active-low and level sensitive. After a CNVSTR reset, the CNVRSEF flag (RSTSRC.6) will read 1 signifying CNVSTR as the reset source; otherwise, this bit reads 0. The state of the /RST pin is unaffected by this reset.
Watchdog Timer Reset
The MCU includes a programmable Watchdog Timer (WDT) running off the system clock. The WDT will force the MCU into the reset state when the watchdog timer overflows. To prevent the reset, the WDT must be restarted by application software before overflow. If the system experiences a software/hardware malfunction preventing the software from restarting the WDT, the WDT will overflow and cause a reset. This should prevent the system from running out of control.
The WDT is automatically enabled and started with the default maximum time interval on exit from all resets. If desired the WDT can be disabled by system software or locked on to prevent accidental disabling. Once locked, the WDT cannot be disabled until the next system reset. The state of the /RST pin is unaffected by this reset.
Watchdog Usage
The WDT consists of a 21-bit timer running from the programmed system clock. The timer measures the period between specific writes to its control register. If this period exceeds the programmed limit, a WDT reset is generated. The WDT can be enabled and disabled as needed in software, or can be permanently enabled if desired. Watchdog features are controlled via the Watchdog Timer Control Register (WDTCN) shown in Table 32.
Enable/Reset WDT
The watchdog timer is both enabled and reset by writing 0xA5 to the WDTCN register. The user's application software should include periodic writes of 0xA5 to WDTCN as needed to prevent a watchdog timer overflow. The WDT is enabled and reset as a result of any system reset.
Disable WDT
Writing 0xDE followed by 0xAD to the WDTCN register disables the WDT. The following code segment illustrates disabling the WDT.
Writing 0xFF to WDTCN locks out the disable feature. Once locked out, the disable operation is ignored until the next system reset. Writing 0xFF does not enable or reset the watchdog timer. Applications always intending to use the watchdog should write 0xFF to WDTCN in their initialization code.
Setting WDT Interval
WDTCN.[2:0] control the watchdog timeout interval. The interval is given by the following equation:
Referring now to
Both oscillators are disabled when the /RST pin is held low. The MCU can run from the internal oscillator 112 permanently, or it can switch to the external oscillator 37 if desired using CLKSL bit in the OSCICN Register 750 (Table 36). The external oscillator requires an external resonator, crystal, capacitor, or RC network connected to the XTAL1/XTAL2 pins. The oscillator circuit must be configured for one of these sources in the OSCXCN register 752 (Table 37). An external CMOS clock can also provide the system clock via overdriving the XTAL1 pin.
If a crystal were used to generate the system clock for the MCU, the circuit would be as shown in
If an external RC network were used to generate the system clock for the MCU, the circuit would be as shown in
If an external capacitor were used to generate the system clock for the MCU, the circuit would be as shown in
Referring back to
The CrossBar 52 assigns the selected internal digital resources to the I/O pins based on the Priority Decode Table 38. The registers XBR0, XBR1, and XBR2, defined in Tables 39, 40 and 41 are used to select an internal digital function or let an I/O pin default to being a Port I/O.
All Port I/Os are 5V tolerant (
Priority Cross Bar Decoder
The Priority CrossBar Decode 404 assigns a priority to each I/O function, starting at the top with the SMBus. When selected, its two signals will be assigned to Pin 0 and 1 of I/O Port 0. The decoder always fills I/O bits from LSB to MSB starting with Port 0, then Port 1, finishing if necessary with Port 2. If the designer chooses not to use a resource, the next function will fill the priority slot. In this way, it is possible to choose only the functions required by the design making full use of the available I/O pins. Also, any extra Port I/O are grouped together for more convenient use in application code.
Registers XBR0, XBR1 and XBR2 are used to assign the digital I/O resources to the physical I/O Port pins. When the SMBus, SPI Bus, or UART is selected, the crossbar 52 assigns all pins associated with the selected bus. It would be impossible for instance to assign the RX pin from the UART function without also assigning the TX function. Standard Port I/Os appear contiguously after the prioritized functions have been assigned. For example, if you choose functions that take the first 14 Port I/O (P0.[7:0], P1.[5:0]), you would have 18 Port I/O left over (P1.[7:6], P2 and P3). The crossbar circuit is described in U.S. patent application Ser. No. 09/583,260, filed May 31, 2000, entitled "Cross-Bar Matrix for Connecting Digital Resources to I10 Pairs of an Integrated Circuit," which is incorporated herein by reference.
Port I/O Initialization
Port I/O initialization is straightforward. Registers XBR0, XBR1 and XBR2 must be loaded with the appropriate values to select the digital I/O functions required by the design. Setting XBR2.7 to 1 enables the CrossBar 52. Until the Crossbar 52 is enabled, the external pins remain as standard Ports in input mode regardless of the XBRn Register settings. For given XBRn Register settings, one can determine the I/O pin-out using the Priority Decode Table; as an alternative, the Configuration Code Generator function of the IDE software will determine the Port I/O pin-assignments based on the XBRn Register settings.
The output driver characteristics of the I/O pins are defined using the Port Configuration Registers PRT0CF, PRT1CF, PRT2CF and PRT3CF (see Tables 43, 45, 48 and 50). Each Port Output driver can be configured as either Open Drain or Push-Pull. This is required even for the digital resources selected in the XBRn registers and is not automatic. The only exception to this is the SMBus (SDA, SCL) and UART Receive (RX) pins which are Open-drain regardless of the PRTnCF settings.
The third and final step is to initialize the individual resources selected using the appropriate setup registers. Initialization procedures for the various digital resources may be found in the detailed explanation of each available function. The reset state of each register is shown in Tables 42-50 that describe each individual register.
The MCU has four byte-wide, bi-directional parallel ports that can be used general purpose I/O. Each port is accessed through a corresponding special function register (SFR) that is both byte addressable and bit addressable. When writing to a port, the value written to the SFR is latched to maintain the output data value at each pin. When reading, the logic levels of the port's input pins are returned regardless of the XBRn settings (i.e. even when the pin is assigned to another signal by the Crossbar, the Port Register can always still read its corresponding Port I/O pin). The exception to this is the execution of the read-modify-write instructions. The read-modify-write instructions when operating on a port SFR are the following: ANL, ORL, XRL, JBC, CPL, INC, DEC, DJNZ and MOV, CLR or SET, when the destination is an individual bit in a port SFR. For these instructions, the value of the register (not the pin) is read, modified, and written back to the SFR.
Serial I/O
Referring now to
Two types of data transfers are possible: data transfers from a master transmitter to an addressed slave receiver, and data transfers from an addressed slave transmitter to a master receiver. The master device initiates both types of data transfers and provides the serial clock pulses. The SMBus interface may operate as a master or a slave. Multiple master devices on the same bus are also supported. If two or more masters attempt to initiate a data transfer simultaneously, an arbitration scheme is employed with a single master always winning the arbitration.
A typical SMBus transaction consists of a START condition, followed by an address byte, one or more bytes of data, and a STOP condition. The address byte and each of the data bytes are followed by an ACKNOWLEDGE bit from the receiver. The address byte consists of a 7-bit address plus a direction bit. The direction bit (R/W) occupies the least-significant bit position of the address. The direction bit is set to logic 1 to indicate a "READ" operation and cleared to logic 0 to indicate a "WRITE" operation. A general call address (0x00+R/W) is recognized by all slave devices allowing a master to address multiple slave devices simultaneously.
All transactions are initiated by the master with one or more addressed slave devices as the target. The master generates the START condition and then transmits the address and direction bit. If the transaction is a WRITE operation from the master to the slave, the master transmits the data a byte at a time waiting for an ACKNOWLEDGE from the slave at the end of each byte. If it is a READ operation, the slave transmits the data waiting for an ACKNOWLEDGE from the master at the end of each byte. At the end of the data transfer, the master generates a STOP condition to terminate the transaction and free the bus.
Serial data is transmitted on SDA while the serial clock is output on SCL. The first byte transmitted contains the address of the target slave device and the data direction bit. In this case the data direction bit (R/W) will be logic 0 to indicate a "WRITE" operation. The master then transmits one or more bytes of serial data. After each byte is transmitted, an acknowledge bit is generated by the slave. START and STOP conditions are output by the master device to indicate the beginning and the end of the serial transfer.
Serial data is received on SDA while the serial clock is output on SCL. The first byte is transmitted by the master and contains the address of the target slave and the data direction bit. In this case the data direction bit (R/W) will be logic 1 to indicate a "READ" operation. Serial data is then received from the slave on SDA while the master outputs the serial clock. One or more bytes of serial data are transmitted by the slave. After each byte is received, an acknowledge bit is transmitted by the master. START and STOP conditions are output by the master to indicate the beginning and end of the serial transfer.
Serial data is transmitted on SDA while the serial clock is received on SCL. First, a byte is received that contains an address and data direction bit. In this case the data direction bit (R/W) will be logic 1 to indicate a "READ" operation. If the received address matches the slave's assigned address (or a general call address is received) one or more bytes of serial data are transmitted to the master. After each byte is received, an acknowledge bit is transmitted by the master. The master outputs START and STOP conditions to indicate the beginning and end of the serial transfer.
Serial data is received on SDA while the serial clock is received on SCL. First, a byte is received that contains an address and data direction bit. In this case the data direction bit (R/W) will be logic 0 to indicate a "WRITE" operation. If the received address matches the slave's assigned address (or a general call address is received) one or more bytes of serial data are received from the master. After each byte is received, an acknowledge bit is transmitted by the slave. START and STOP conditions are output by the master to indicate the beginning and end of the serial transfer.
A master may start a transfer only if the bus is free. The bus is free after a STOP condition or after the SCL and SDA lines remains high for a specified time. Two or more master devices may attempt to generate a START condition at the same time. Since the devices that generated the START condition may not be aware that other masters are contending for the bus, an arbitration scheme is employed. The master devices continue to transmit until one of the masters transmits a HIGH level, while the other(s) master transmits a LOW level on SDA. The first master(s) transmitting the HIGH level on SDA looses the arbitration and is required to give up the bus.
SMBus provides a clock synchronization mechanism, similar to I2C, which allows devices with different speed capabilities to coexist on the bus. A clock-low extension is used during a transfer in order to allow slower slave devices to communicate with faster masters. The slave can hold the SCL line LOW to extend the clock low period, effectively decreasing the serial clock frequency.
If the SCL line is held low by a slave device on the bus, no further communication is possible. Furthermore, the master cannot force the SCL line high to correct the error condition. To solve this problem, the SMBus protocol specifies that devices participating in a transfer must detect any clock cycle held low longer than 25 ms as a "timeout" condition. Devices that have detected the timeout condition must reset the communication no later than 10 ms after detecting the timeout condition.
One of the MCU's general-purpose timers, operating in 16-bit auto-reload mode, can be used to monitor the SCL line for this timeout condition. Timer 3 is specifically designed for this purpose.
The SMBus specification stipulates that if a device holds the SCL and SDA lines high for more that 50 usec, the bus is designated as free. The SMB0CR register is used to detect this condition when the FTE bit in SMB0CN is set, thereby setting the SI bit in SMB0CN if this event is detected.
SMBus Special Function Registers
The SMBus serial interface is accessed and controlled through five SFRs: SMB0CN Control Register, SMB0CR Clock Rate Register, SMB0ADR Address Register, SMB0DAT Data Register and SMB0STA Status Register. The system device may have one or more SMBus serial interfaces implemented. The five special function registers related to the operation of the SMBus interface are described in the following section.
Control Register
The SMBus Control register SMB0CN (Table 51) is used to configure and control the SMBus interface. All of the bits in the register can be read or written by software. Two of the control bits are also affected by the SMBus hardware. The Serial Interrupt flag (SI, SMB0CN.3) is set to logic 1 by the hardware when a valid serial interrupt condition occurs. It can only be cleared by software. The Stop flag (STO, SMB0CN.4) is cleared to logic 0 by hardware when a STOP condition is present on the bus.
Setting the ENSMS flag to logic 1 enables the SMBus interface. Clearing the ENSMB flag to logic 0 disables the SMBus interface and removes it from the bus. Momentarily clearing the ENSMB flag and then resetting it to logic 1 will reset a SMBus communication. However, ENSMB should not be used to temporarily remove a device from the bus since the bus state information will be lost. Instead, the Assert Acknowledge (AA) flag should be used to temporarily remove the device from the bus (see description of AA flag below).
Setting the Start flag (STA, SMB0CN.5) to logic 1 will put the SMBus in a master mode. If the bus is free, the SMBus hardware will generate a START condition. If the bus is not free, the SMBus hardware waits for a STOP condition to free the bus and then generates a START condition after a 5 us delay per the SMB0CR value. (In accordance with the SMBus protocol, the SMBus interface also considers the bus free if the bus is idle for 50 us and no STOP condition was recognized.) If STA is set to logic 1 while the SMBus is in master mode and one or more bytes have been transferred, a repeated START condition will be generated.
When the Stop flag (STO, SMB0CN.4) is set to logic 1 while the SMBus interface is in master mode, the hardware generates a STOP condition on the SMBus. In a slave mode, the STO flag may be used to recover from an error condition. In this case, a STOP condition is not generated on the SMBus, but the SMBus hardware behaves as if a STOP condition has been received and enters the "not addressed" slave receiver mode. The SMBus hardware automatically clears the STO flag to logic 0 when a STOP condition is detected on the bus.
The Serial Interrupt flag (SI, SMB0CN.3) is set to logic 1 by hardware when the SMBus interface enters one of 27 possible states. If interrupts are enabled for the SMBus interface, an interrupt request is generated when the SI flag is set. The SI flag must be cleared by software. If SI is set to logic 1 while the SCL line is low, the clock-low period of the serial clock will be stretched and the serial transfer is suspended. A high level on SCL is not affected by the setting of the SI flag.
The Assert Acknowledge flag (AA, SMB0CN.2) is used to set the level of the SDA line during the acknowledge clock cycle on the SCL line. Setting the AA flag to logic 1 will cause an ACKNOWLEDGE (low level on SDA) to be sent during the acknowledge cycle if the device has been addressed. Setting the AA flag to logic 0 will cause a NOT ACKNOWLEDGE (high level on SDA) to be sent during acknowledge cycle. After the transmission of a byte in slave mode, the slave can be temporarily removed from the bus by clearing the AA flag. The slave's own address and general call address will be ignored. To resume operation on the bus, the AA flag must be reset to logic 1 to allow the slave's address to be recognized.
Setting the SMBus Free Timer Enable bit (FTE, SMB0CN.1) to logic 1 enables the timer in SMB0CR. When SCL goes high, the timer in SMB0CR counts up. If it overflows, the bus will be freed from being be driven by the master. The bus free period should be less than 50 usec (see Table 52, SMBus Clock Rate Register).
Setting the SMBus timeout enable bit to logic 1 enables Timer 3 to count up when the SCL line is high and Timer 3 is enabled. If Timer 3 overflows, a Timer 3 interrupt will be generated, which will alert the CPU that a SMBus SCL low timeout has occurred.
Clock Rate Register
Data Register
The SMBus Data register SMB0DAT (Table 53) holds a byte of serial data to be transmitted or one that has just been received. Software can read or write to this register while the SI flag is set to logic 1. Data remains stable in the register as long as SI is set to logic 1. Software can safely read or write to the data register when the SI flag is set. Software should not attempt to access the SMB0DAT register when the SMBus is enabled and the SI flag is cleared to logic 0 since the hardware may be in the process of shifting a byte of data in or out of the register.
Data in SMB0DAT is always shifted out MSB first. After a byte has been received, the first bit of received data is located at the MSB of SMB0DAT. While data is being shifted out, data on the bus is simultaneously being shifted in. Therefore, SMB0DAT always contains the last data byte present on the bus. Thus, in the event of lost arbitration, the transition from master transmitter to slave receiver is made with the correct data in SMB0DAT.
Address Register
The SMB0ADR Address register (Table 54) holds the slave address for the SMBus interface. In slave mode, the seven most-significant bits hold the 7-bit slave address. The least significant bit, bit 0, is used to enable the recognition of the general call address (0x00). If bit 0 is set to logic 1, the general call address will be recognized. Otherwise, the general call address is ignored. The contents of this register are ignored when the SMBus hardware is operating in master mode.
Status Register
The SMB0STA Status register (Table 55) holds an 8-bit status code indicating the current state of the SMBus. There are 28 possible SMBus states, each with a corresponding unique status code. The five most significant bits of the status code vary while the three least-significant bits of a valid status code are fixed at zero when SI=1. Therefore, all possible status codes are multiples of eight. This facilitates the use of status codes in software as an index used to branch to appropriate service routines (allowing 8 bytes of code to service the state or jump to a more extensive service routine).
For the purposes of user software, the contents of the SMB0STA register is only defined when the SI flag is logic 1. Software should never write to the SMB0STA register. Doing so will yield indeterminate results. The 28 SMBus states, along with their corresponding status codes, are given in Table 56.
Referring now to
The four signals used by the SPI on lines 800 (MOSI, MISO, SCK, NSS) are described below.
The master-out, slave-in (MOSI) signal is an output from a master device and an input to slave devices. It is used to serially transfer data from the master to the slave. Data is transferred most-significant bit first.
The master-in, slave-out (MISO) signal is an output from a slave device and an input to the master device. It is used to serially transfer data from the slave to the master. Data is transferred most-significant bit first. A SPI slave places the MISO pin in a high-impedance state when the slave is not selected.
The serial clock (SCK) signal is an output from the master device and an input to slave devices. It is used to synchronize the transfer of data between the master and slave on the MOSI and MISO lines.
The slave select (NSS) signal is an input used to select the SPI module when in slave mode by a master, or to disable the SPI module when in master mode. When in slave mode, it is pulled low to initiate a data transfer and remains low for the duration of the transfer.
Only a SPI master device can initiate a data transfer. The SPI is placed in master mode by setting the Master Enable flag (MSTEN, SPI0CN.1). Writing a byte of data to the SPI data register (SPI0DAT) 802 (Table 60) when in Master Mode starts a data transfer. The SPI master immediately shifts out the data serially on the MOSI line while providing the serial clock on SCK. The SPIF (SPI0CN.7) flag from register 804 (Table 58) is set to logic 1 at the end of the transfer. If interrupts are enabled, an interrupt request is generated when the SPIF flag is set. The SPI master can be configured to shift in/out from one to eight bits in a transfer operation in order to accommodate slave devices with different word lengths. The SPIFRS bits in an SPI Configuration Register 806 (Table 57) (SPI0CFG[2:0]) are used to select the number of bits to shift in/out in a transfer operation.
While the SPI master transfers data to a slave on the MOSI line, the addressed SPI slave device simultaneously transfers the contents of its shift register to the SPI master on the MISO line in a full-duplex operation. The data byte received from the slave replaces the data in the master's data register. Therefore, the SPIF flag serves as both a transmit-complete and receive-data-ready flag. The data transfer in both directions is synchronized with the serial clock generated by the master.
The SPI data register is double buffered on reads, but not on a write. If a write to SPIODAT 802 is attempted during a data transfer, the WCOL flag (SPI0CN.6) will be set to logic 1 and the write is ignored. The current data transfer will continue uninterrupted. A read of the SPI data register by the system controller actually reads the receive buffer. If the receive buffer still holds unread data from a previous transfer when the last bit of the current transfer is shifted into the SPI shift register, a receive overrun occurs and the RXOVRN flag (SPI0CN.4) is set to logic 1. The new data is not transferred to the receive buffer, allowing the previously received data byte to be read. The data byte causing the overrun is lost.
When the SPI is enabled and not configured as a master, it will operate as an SPI slave. Another SPI device acting as a master will initiate a transfer by driving the NSS signal low. The master then shifts data out of the shift register on the MISO pin using the serial clock. The SPIF flag is set to logic 1 at the end of a data transfer (when the NSS signal goes high). The slave can load its shift register for the next data transfer by writing to the SPI data register. The slave must make the write to the data register at least one SPI serial clock cycle before the master starts the next transmission. Otherwise, the byte of data already in the slave's shift register will be transferred.
Multiple masters may reside on the same bus. A Mode Fault flag (MODF, SPI0CN.5) is set to logic 1 when the SPI is configured as a master (MSTEN=1) and its slave select signal NSS is pulled low. In a multiple-master environment, the system controller should check the state of the SLVSEL flag (SPI0CN.2) to ensure the bus is free before setting the MSTEN bit and initiating a data transfer.
Serial Clock Timing
As shown in
The SPI Clock Rate Register (SPI0CKR) 810 (Table 59) controls the master mode serial clock frequency. This register is ignored when operating in slave mode.
SPI Special Function Registers
The SPI is accessed and controlled through four special function registers in the system controller: SPI0CN Control Register 800, SPI0DAT Data Register 802, SPI0CFG Configuration Register 806, and SPI0CKR Clock Rate Register 810.
Referring now to
The UART has an associated Serial Control Register (SCON) 820 (Table 62) and a Serial Data Buffer (SBUF) 822 in the SFRs. The single SBUF 822 location provides access to both transmit and receive registers. Reads access the Receive register and writes access the Transmit register automatically.
The UART is capable of generating interrupts if enabled. The UART has two sources of interrupts: a Transmit Interrupt flag, TI (SCON.1) set when transmission of a data byte is complete, and a Receive Interrupt flag, RI (SCON.0) set when reception of a data byte is complete. The UART interrupt flags are not cleared by hardware when the CPU vectors to the interrupt service routine. They must be cleared manually by software. This allows software to determine the cause of the UART interrupt (transmit complete or receive complete).
UART Operational Modes
The UART provides four operating modes (one synchronous and three asynchronous) selected by setting configuration bits in the SCON register. These four modes offer different baud rates and communication protocols. The four modes are summarized in Table 15.1 below.
Mode 0 provides synchronous, half-duplex communication. Serial data is transmitted and received on the RX pin. The TX pin provides the shift clock for both transmit and receive. The MCU must be the master since it generates the shift clock for transmission in both directions (
Eight data bits are transmitted/received, LSB first (
Mode 1: 8-Bit UART, Variable Baud Rate
Mode 1 provides standard asynchronous, full duplex communication using a total of 10 bits per data byte: one start bit, eight data bits (LSB first), and one stop bit; the timing diagram illustrated in
Data transmission begins when an instruction writes a data byte to the SBUF register. The TI Transmit Interrupt Flag (SCON.1) is set at the end of the transmission (the beginning of the stop-bit time). Data reception can begin any time after the REN Receive Enable bit (SCON.4) is set to logic 1. After the stop bit is received, the data byte will be loaded into the SBUF receive register if the following conditions are met: RI must be logic 0, and if SM2 is logic 1, the stop bit must be logic 1.
If these conditions are met, the eight bits of data is stored in SBUF, the stop bit is stored in RB8 and the RI flag is set. If these conditions are not met, SBUF and RB8 will not be loaded and the RI flag will not be set. An interrupt will occur if enabled when either TI or RI are set.
The baud rate generated in Mode 1 is a function of timer overflow. The UART can use either Timer 1 or Timer 2 operating in auto-reload mode to generate the baud rate. On each timer overflow event (a rollover from all ones—0xFF for Timer 1, 0xFFFF for Timer 2—to zero) a clock is sent to the baud rate circuit. This clock is divided by 16 to generate the baud rate.
Timer 1 should be configured for 8-bit Counter/Timer with Auto-Reload mode and its interrupt disabled when used as a baud rate generator. The combination of system clock frequency and the reload value stored in TH1 determine the baud rate as follows:
The SMOD bit (PCON.7) selects whether or not to divide the Timer 1 overflow rate by two. On reset, the SMOD bit is logic 0, thus selecting the lower speed baud rate by default. Selecting the timebase used by Timer 1 allows further control of baud rate generation. Using the system clock divided by one (setting T1M in CKCON) changes the twelve in the denominator of the equation above to a one.
To use Timer 2 for baud rate generation, configure the timer Baud Rate Generator mode and set RCLK and/or TCLK to logic 1. Setting RCLK and/or TCLK automatically disables Timer 2 interrupts and configures Timer 2 to use the system clock divided by two as its timebase. If a different timebase is required, setting the C/T2 bit to logic 1 will allow the timebase to be derived from a clock supplied to the external input pin T2. The combination of clock frequency and the reload value stored in capture registers determine the baud rate as follows:
Mode 2 provides asynchronous, full-duplex communication using a total of eleven bits per data byte: a start bit, 8 data bits (LSB first), a programmable ninth data bit, and a stop bit, the timing diagram therefore illustrated in
Data transmission begins when an instruction writes a data byte to the SBUF register. The TI Transmit Interrupt Flag (SCON.1) is set at the end of the transmission (the beginning of the stop-bit time). Data reception can begin any time after the REN Receive Enable bit (SCON.4) is set to logic 1. After the stop bit is received, the data byte will be loaded into the SBUF receive register if the following conditions are met: RI must be logic 0, and if SM2 is logic 1, the 9th bit must be logic 1.
If these conditions are met, the eight bits of data is stored in SBUF, the ninth bit is stored in RB8 and the RI flag is set. If these conditions are not met, SBUF and RB8 will not be loaded and the RI flag will not be set. An interrupt will occur if enabled when either TI or RI are set.
The baud rate in Mode 2 is a direct function of the system clock frequency as follows:
The SMOD bit (PCON.7) selects whether to divide SYSCLK by 32 or 64. In the formula, 2 is raised to the power SMOD, resulting in a baud rate of either 1/32 or 1/64 of the system clock frequency. On reset, the SMOD bit is logic 0, thus selecting the lower speed baud rate by default.
Mode 3: 9-Bit UART, Variable Baud Rate
Mode 3 is the same as Mode 2 in all respects except the baud rate is variable. The baud rate is determined in the same manner as for Mode 1. Mode 3 operation transmits 11 bits: a start bit, 8 data bits (LSB first), a programmable ninth data bit, and a stop bit. Timer 1 or Timer 2 overflows generate the baud rate just as with Mode 1. In summary, Mode 3 transmits using the same protocol as Mode 2 but with Mode 1 baud rate generation.
The Timer Mode Register (T2CON) 824 is illustrated in Table 64.
Multiprocessor Communications
Modes 2 and 3 support multiprocessor communication between a master processor and one or more slave processors by special use of the ninth data bit, as illustrated in
Setting the SM2 bit (SCON.5) of a slave processor configures its UART such that when a stop bit is received, the UART will generate an interrupt only if the ninth bit is logic one (RB8=1) signifying an address byte has been received. In the UART's interrupt handler, software will compare the received address with the slave's own assigned 8-bit address. If the addresses match, the slave will clear its SM2 bit to enable interrupts on the reception of the following data byte(s). Slaves that weren't addressed leave their SM2 bits set and do not generate interrupts on the reception of the following data bytes, thereby ignoring the data. Once the entire message is received, the addressed slave resets its SM2 bit to ignore all transmissions until it receives the next address byte.
Multiple addresses can be assigned to a single slave and/or a single address can be assigned to multiple slaves, thereby enabling "broadcast" transmissions to more than one slave simultaneously. The master processor can be configured to receive all transmissions or a protocol can be implemented such that the master/slave role is temporarily reversed to enable half-duplex transmission between the original master and slave(s).
The Microcontroller 40 implements four counter/timers: three are 16-bit counter/timers compatible with those found in the standard 8051, and one is a 16-bit timer for use with the ADC, SMBus, or for general purpose use. These can be used to measure time intervals, count external events and generate periodic interrupt requests. Timer 0 and Timer 1 are nearly identical and have four primary modes of operation. Timer 2 offers additional capabilities not available in Timers 0 and 1. Timer 3 is similar to Timer 2, but without the capture or Baud Rate Generator modes. Table 65 illustrates the timers.
When functioning as a timer, the counter/timer registers are incremented on each clock tick. Clock ticks are derived from the system clock divided by either one or twelve as specified by the Timer Clock Select bits (T2M-T0M) in CKCON. The twelve-clocks-per-tick option provides compatibility with the older generation of the 8051 family. Applications that require a faster timer can use the one-clock-per-tick option.
When functioning as a counter, a counter/timer register is incremented on each high-to-low transition at the selected input pin. Events with a frequency of up to one-fourth the system clock's frequency can be counted. The input signal need not be periodic, but it should be held at a given level for at least two full system clock cycles to ensure the level is sampled.
Timer 0 and Timer 1
Timer 0 and Timer 1 are accessed and controlled through SFRs. Each counter/timer is implemented as a 16-bit register accessed as two separate bytes: a low byte (TL0 or TL1) and a high byte (TH0 or TH1). The Counter/Timer Control (TCON) register 830 (Table 66) is used to enable Timer 0 and Timer 1 as well as indicate their status. Both counter/timers operate in one of four primary modes selected by setting the Mode Select bits M1-M0 in the Counter/Timer Mode (TMOD) register. Each timer can be configured independently. Following is a detailed description of each operating mode.
Mode 0: 13-bit Counter/Timer
Timer 0 and Timer 1 operate as a 13-bit counter/timer in Mode 0. The following describes the configuration and operation of Timer 0, illustrated in
The TH0 register holds the eight MSBs of the 13-bit counter/timer. TL0 holds the five LSBs in bit positions TL0.4-TL0.0. The three upper bits of TL0 (TL0.7-TL0.5) are indeterminate and should be masked out or ignored when reading. As the 13-bit timer register increments and overflows from 0x1FFF (all ones) to 0x0000, the timer overflow flag TF0 (TCON.5) is set and an interrupt will occur if enabled.
The C/T0 bit (TMOD.2) selects the counter/timer's clock source. Clearing C/T selects the system clock as the input for the timer. When C/T0 is set to logic 1, high-to-low transitions at the selected input pin increment the timer register.
Setting the TR0 bit (TCON.4) enables the timer when either GATE0 (TMOD.3) is 0 or the input signal /INT0 is logic-level one. Setting GATE 0 to logic 1 allows the timer to be controlled by the external input signal /INT0, facilitating pulse width measurements. Table 67 illustrates the TRO bit/Gate lists.
TL1 and TH1 form the 13-bit register for Timer 1 in the same manner as described above for TL0 and TH0. Timer 1 is configured and controlled using the relevant TCON and TMOD bits just as with Timer 0.
Mode 1: 16-bit Counter/Timer
Mode 1 operation is the same as Mode 0, except that the counter/timer registers use all 16 bits. The counter/timers are enabled and configured in Mode 1 in the same manner as for Mode 0.
Mode 2: 8-bit Counter/Timer with Auto-Reload
Mode 2 configures Timer 0 and Timer 1 to operate as 8-bit counter/timers with automatic reload of the start value, and is illustrated in
Mode 3: Two 8-Bit Counter/Timers (Timer 0 Only)
Timer 0 and Timer 1 behave differently in Mode 3. Timer 0 is configured as two separate 8-bit counter/timers held in TL0 and TH0, and is illustrated in
Timer 1 is inactive in Mode 3, so with Timer 0 in Mode 3, Timer 1 can be turned off and on by switching it into and out of its Mode 3. When Timer 0 is in Mode 3, Timer 1 can be operated in Modes 0, 1 or 2, but cannot be clocked by external signals nor set the TF1 flag and generate an interrupt. However, the Timer 1 overflow can be used for baud rate generation.
The Timer 0 and Timer 1 operations are illustrated in Tables 70-73.
Timer 2
Timer 2 is a 16-bit counter/timer formed by the two 8-bit SFRs: TL2 (low byte) and TH2 (high byte). As with Timers 0 and 1, Timer 2 can use either the system clock or transitions on an external input pin as its clock source. The Counter/Timer Select bit C/T2 bit (T2CON.1) selects the clock source for Timer 2. Clearing C/T2 selects the system clock as the input for the timer (divided by either one or twelve as specified by the Timer Clock Select bit T2M in CKCON). When C/T2 is set to 1, high-to-low transitions at the T2 input pin increment the counter/timer register. Timer 2 can also be used to start an ADC Data Conversion.
Timer 2 offers capabilities not found in Timer 0 and Timer 1. It operates in one of three modes: 16-bit Counter/Timer with Capture, 16-bit Counter/Timer with Auto-Reload or Baud Rate Generator Mode. Timer 2's operating mode is selected by setting configuration bits in the Timer 2 Control (T2CON) register (Table 74). Below is a summary of the Timer 2 operating modes and the T2CON bits used to configure the counter/timer. Detailed descriptions of each mode follow in Table 68.
In this mode, illustrated in
Timer 2 can use either SYSCLK, SYSCLK divided by 12, or high-to-low transitions on the T2 input pin as its clock source when operating in Counter/Timer with Capture mode. Clearing the C/T2 bit (T2CON.1) selects the system clock as the input for the timer (divided by one or twelve as specified by the Timer Clock Select bit T2M in CKCON 844 (Table 69)). When C/T2 is set to logic 1, a high-to-low transition at the T2 input pin increments the counter/timer register. As the 16-bit counter/timer register increments and overflows from 0xFFFF to 0x0000, the TF2 timer overflow flag (T2CON.7) is set and an interrupt will occur if the interrupt is enabled.
Counter/Timer with Capture mode is selected by setting the Capture/Reload Select bit CP/RL2 (T2CON.0) and the Timer 2 Run Control bit TR2 (T2CON.2) to logic 1. The Timer 2 External Enable EXEN2 (T2CON.3) must also be set to logic 1 to enable a capture. If EXEN2 is cleared, transitions on T2EX will be ignored.
Mode 1: 16-bit Counter/Timer with Auto-Reload
The Counter/Timer with Auto-Reload mode sets the TF2 timer overflow flag when the counter/timer register overflows from 0xFFFF to 0x0000, illustrated in
Counter/Timer with Auto-Reload mode is selected by clearing the CP/RL2 bit. Setting TR2 to logic 1 enables and starts the timer. Timer 2 can use either the system clock or transitions on an external input pin as its clock source, as specified by the C/T2 bit. If EXEN2 is set to logic 1, a high-to-low transition on T2EX will also cause Timer 2 to be reloaded. If EXEN2 is cleared, transitions on T2EX will be ignored.
16.2.3. Mode 2: Baud Rate Generator
Timer 2 can be used as a baud rate generator for the serial port (UART) when the UART is operated in modes 1 or 3, illustrated in
The Baud Rate Generator mode is selected by setting RCLK (T2CON.5) and/or TCLK (T2CON.4) to logic one. When RCLK or TCLK is set to logic 1, Timer 2 operates in the auto-reload mode regardless of the state of the CP/RL2 bit. The baud rate for the UART, when operating in mode 1 or 3, is determined by the Timer 2 overflow rate:
Note, in all other modes, the timebase for the timer is the system clock divided by one or twelve as selected by the T2M bit in CKCON. However, in Baud Rate Generator mode, the timebase is the system clock divided by two. No other divisor selection is possible. If a different time base is required, setting the C/T2 bit to logic 1 will allow the timebase to be derived from the external input pin T2. In this case, the baud rate for the UART is calculated as:
As explained above, in Baud Rate Generator mode, Timer 2 does not set the TF2 overflow flag and therefore cannot generate an interrupt. However, if EXEN2 is set to logic 1, a high-to-low transition on the T2EX input pin will set the EXF2 flag and a Timer 2 interrupt will occur if enabled. Therefore, the T2EX input may be used as an additional external interrupt source.
The Timer 2 Capture Registers are illustrated in Tables 75-78.
Programmable Counter Array
The Programmable Counter Array (PCA) provides enhanced timer functionality while requiring less CPU intervention than the standard 8051 counter/timers. The PCA consists of a dedicated 16-bit counter/timer and five 16-bit capture/compare modules. Each capture/compare module has its own associated I/O line (CEXn) which is routed through the Crossbar to Port I/O when enabled (referring back to
Capture/Compare Modules
Each module can be configured to operate independently in one of four operation modes: Edge-triggered Capture, Software Timer, High Speed Output, or Pulse Width Modulator. Each module has Special Function Registers (SFRs) associated with it in the Microcontroller 40 system controller. These registers are used to exchange data with a module and configure the module's mode of operation.
Table 80 summarizes the bit settings in the PCA0CPMn registers used to place the PCA capture/compare modules into different operating modes. Setting the ECCFn bit in a PCA0CPMn register enables the module's CCFn interrupt. Note: PCA0 interrupts must be globally enabled before individual CCFn interrupts are recognized. PCA0 interrupts are globally enabled by setting the EA bit (IE.7) and the EPCA0 bit (EIE1.3) to logic 1.
In this mode, illustrated in
Software Timer (Compare) Mode
In Software Timer mode, illustrated in
High Speed Output Mode
In this mode, illustrated in
Pulse Width Modulator Mode
All of the modules can be used independently to generate pulse width modulated (PWM) outputs on their respective CEXn pin. The PWM mode is illustrated in
PCA Counter/Timer
The 16-bit PCA counter/timer, illustrated in
When the counter/timer overflows from 0xFFFF to 0x0000, the Counter Overflow Flag (CF) in PCA0MD 866 is set to logic 1 and an interrupt request is generated if CF interrupts are enabled. Setting the ECF bit in PCA0MD to logic 1 enables the CF flag to generate an interrupt request. The CF bit is not automatically cleared by hardware when the CPU vectors to the interrupt service routine, and must be cleared by software. (Note: PCA0 interrupts must be globally enabled before CF interrupts are recognized. PCA0 interrupts are globally enabled by setting the EA bit (IE.7) and the EPCA0 bit in EIE1 to logic 1.) Clearing the CIDL bit in the PCA0MD register allows the PCA to continue normal operation while the microcontroller core is in Idle mode. The control register (PCA)CN) settings are set forth in Table 80 with the PCA0MD mode register settings illustrated in Table 81.
The MCU has an on-chip JTAG interface and logic to support boundary scan for production and in-system testing, Flash read/write operations, and non-intrusive in-circuit emulation. The JTAG interface is fully compliant with the IEEE 1149.1 specification. Access of the JTAG Instruction Register (IR) and Data Registers (DR) are as described in the Test Access Port and Operation of the IEEE 1149.1 specification.
The JTAG interface is via four dedicated pins 44 on the MCU, which are TCK, TMS, TDI, and TDO.
The PCA0CPMn PCA Capture/Compare registers are illustrated in Table 82, with the PCA counter operation illustrated in Tables 83-86.
Through the 16-bit JTAG Instruction Register (IR), any of the eight instructions shown in Table 87 can be commanded. There are three DR's associated with JTAG Boundary-Scan, and four associated with Flash read/write operations on the MCU.
Boundary Scan
The DR in the Boundary Scan path is an 87-bit shift register. The Boundary DR provides control and observability of all the device pins as well as the SFR bus and Weak Pullup feature via the EXTEST and SAMPLE commands.
The EXTEST instruction is accessed via the IR. The Boundary DR provides control and observability of all the device pins as well as the SFR bus and Weak Pullup feature. All on-chip latches are set to one.
SAMPLE Instruction
The SAMPLE instruction is accessed via the IR. The Boundary DR provides observability and presetting of the scan-path latches.
BYPASS Instruction
The BYPASS instruction is accessed via the IR. It provides access to the standard JTAG Bypass data register.
IDCODE Instruction
The IDCODE instruction is accessed via the IR. It provides access to the 32-bit Device ID register. The Flash memory can be programmed directly over the JTAG interface using the Flash Control, Flash Data, Flash Address, and Flash Scale registers. These Data Registers are accessed via the JTAG Instruction Register.
Emulation Support
The MCU has on-chip JTAG and emulation logic that provide non-intrusive, full speed, in-circuit emulation using the production part installed in the end application using the four pin JTAG I/F. The emulation system supports inspection and modification of memory and registers, breakpoints, and single stepping. No additional target RAM, program memory, or communications channels are required. All the digital and analog peripherals are functional and work correctly (remain in sync) while emulating. The WDT is disabled when the MCU is halted during single stepping or at a breakpoint.
Although the preferred embodiment has been described in detail, it should be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.