relative or absolute addressing RETC: return from subroutine on condition True (zero, greater-than, less-than or unconditional) RETE: return from interrupt on condition True (zero, greater-than, less-than or unconditional) ZBSR: branch to subroutine relative to address zero BSXA: branch to subroutine indexed Only the branch instructions using absolute addressing used all 15 bits of the address field as address. Using such a branch instruction was, therefore, the only way to set the two bits in the page register (controlling bits 14 and 13 of the address bus) and changing the current 8 KB page. Versions 2650 original version with 1.25 MHz maximum clock frequency 2650A improved version (minor fabrication changes to improve stability) 1.25 MHz maximum clock frequency 2650A-1 as 2650A with 2 MHz maximum clock frequency 2650B 2650B-1 as 2650B with 2 MHz maximum clock frequency The 2650B had the following changes and improvements over the 2650A: Two new signals "Bus Enable" on pin 15 and "Cycle Last" on pin 25. Program Status Word Upper bits 3 and 4 are settable and testable user flags (unused on the 2650A). Two new instructions to save and restore the lower status register in order to simplify interrupt processing. Single byte register R0 instructions execute faster (one cycle rather than two). Second sources In 1975, Signetics was sold to Philips and the 2650 was later incorporated into the Philips Semiconductors line. They made a version of the 2650 called the MAB2650A. Valvo, a subsidiary of Philips, sold the 2650 in Germany. Valvo also sold the VA200 single board (Eurocard) 2650 computer with 4 KB PROM/EPROM, 1 KB RAM and four I/O ports. Other producers of licensed copies of the chip were Harris and Intersil. Peripheral chips The 2650 came with a full complement of peripheral chips: 2621 Video Encoder (PAL) 2622 Video Encoder (NTSC) 2636 Programmable Video Interface 2637 Universal Video Interface 2651 Programmable Communication Interface 2652 Multi-Protocol Communications Circuit (incl. Synchronous Data Link Control (SDLC)) 2653 Polynomial Generator / Checker 2655 Programmable Peripheral Interface 2656 SMI (System memory interface) 2657 Direct Memory Access 2661 Enhanced Programmable Communication Interface (EPCI) 2670 Display Character and Graphics Generator 2671 Programmable Keyboard and Communications Controller 2672 Programmable Video Timing Controller 2673 Video Attributes Controller Many of these peripheral chips were designed so they could also be used with other microprocessors, for example the datasheet of the 2672 suggests using it with an Intel 8048 microcontroller. Philips