Sound The CoCo has two methods of making sound: a 6-bit Digital-to-analog converter and a separate 1-bit sound source. Cassette playback or an analog signal can be also be routed from the cartridge port to the TV speaker. PIAs There are two Peripheral Interface Adapter chips in all CoCo models. The PIAs are dedicated to I/O operations such as driving the internal 6-bit Digital-to-analog converter, controlling the relay for the cassette motor, reading the keyboard, controlling the VDG mode pins, and accessing the RS-232 serial I/O port. The earliest CoCo models have two standard 6821 chips. Later, after changes in the keyboard design, the 6822 IIA (Industrial Interface Adapter) was used instead. The 6822 was eventually discontinued by Motorola, but was produced for Tandy as an application-specific integrated circuit with the part number SC67331P. Interface to external peripherals Due to the CoCo's design, the MPU encounters no wait states in normal operation. This means that precise software controlled timing loops are easily implemented. This is important since the CoCo has no specialized hardware for any I/O. All I/O operations, such as cassette reading and writing, serial I/O, scanning the keyboard, and reading the position of the joysticks, must be done entirely in software. This reduces hardware cost but reduces system performance as the MPU is unavailable during these operations. As an example, the CoCo cassette interface is perhaps one of the fastest available (1500 bits/s) but it does so entirely under software control. While reading or writing a cassette the CoCo has no CPU time free for other tasks. They must wait until an error occurs or all the data needed is read. CoCo 3 hardware changes In the CoCo 3, a new VLSI ASIC called (officially) the Advanced Color Video Chip (ACVC) or (unofficially) the Graphics Interrupt Memory Enhancer (GIME), integrated the functions of the SAM and VDG while enhancing the capabilities of both. The CoCo 3 supports 40- and 80-column text and the ability to run at 1.8 MHz without loss of video. The processor was changed to the 68B09E and the PIA was changed to the 68B21, which are 2 MHz parts. Discontinuation On October 26, 1990, Tandy announced that the CoCo 3 would be dropped from its computer line. Wayne Green wrote in 80 Micro in December 1982 that Tandy had "virtually abandoned" the Color Computer. As with its other computers, Tandy attempted to monopolize hardware