Texas Instruments TMS9980 (TMS9980A) microprocessor family
Texas Instruments TMS9980 (TMS9080A) is a 16-bit microprocessor based on TMS 9900 memory-to-memory architecture. The idea behind this architecture is that the microprocessor doesn't store the contents of CPU registers in on-chip memory, and uses part of main memory for this purpose. If necessary, the CPU can change the address of the register set in main memory by executing only one instruction. This makes saving and restoring of the contents of all CPU registers very fast and very simple, which is important for interrupt handling and for program subroutines. The disadvantage of this architecture is that the processor speed becomes more dependent on memory speed. When used with fast memory (no wait states), the TMS9980A CPU can execute more than 100,000 arithmetic instructions per second. Each additional wait state slows down the CPU by 30%.
The TMS9980 is fully object-code compatible with the TMS 9900 microprocessors, albeit it's approximately 33% slower than the TMS9900 at the same frequency. The slower execution speed of the TMS9980 is exclusively due to its more narrow, 8-bit external data bus.
The TMS9980A was manufactured in 40-pin DIP package.