Texas Instruments TMS9900

The TMS 9900 was a 1976 imagined 16 -bit processor from Texas Instruments (TI), which is known primarily for use in the home computers of the TI -99 series. He was one of the first 16 -bit microprocessors and designed by the design as a single-chip version of the TI -990 minicomputer series.

A special feature of the TMS9900 is that the registers are located in a part of the external RAM. A workspace pointer (WP) called internal register points to a range of 16 16- bit words ( the workspace), which can be used as registers. This provides a quick change of different register sets is possible, which is especially helpful for multitasking applications and the interrupt, since it avoids the saving of registers during a context switch.

Furthermore, the TMS9900 has in its command set over an unusual command which is referred to as 'X'. In this case, a command is executed which is located at a location specified by a register address in the memory. In contrast to the usual branch instructions then the program continues right after the 'X' command and not continued after the jump address. This allowed for the time already single-step debugging run purely with software, ie without the need for additional special hardware for this.