Texas Instruments TMS9900

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The Texas Instruments TMS9900 is a 16-bit microprocessor monolithic integrated circuit introduced in 1976.

The architecture is purely 16-bit, with a 16-bit data bus and a 15-bit address bus for a 32kWords (64KBytes) capacity. Addresses refer to bytes with big-endian ordering convention (TI labeled the most significant address and data lines "A0" and "D0", respectively).

There are three internal 16-bit registers (program counter, status register, and workspace pointer). The latter points to a base address in external RAM where the processor's 16 general-purpose user registers (each 16 bits wide) are kept.

There is no stack and no stack pointer; instead, the TMS9900 has branch instructions that save the program counter to a register and change the register context. Register context switch is also used for interrupts. The processor can be paused with the address bus tri-stated for external direct memory access (DMA).

The TMS9900 was implemented in an N-channel Si-gate MOS process and requires 5 V, −5 V and +12 V supplies. It came packaged in a 64-pin, 0.9" wide DIP.

Maximum clock frequency is 3 MHz, often generated from a 48 MHz oscillator using a TIM9904 (74LS362) clock generator, because the CPU requires four non-overlapping clock phases. The shortest instructions require eight clock cycles or 2.7 μs to complete.

Pinout (click to enlarge)

The TMS9980 and TMS9981 were versions with an external 8-bit data bus. The TMS9989 is an improved 9900 that saw some appication in military hardware.


Used in

Some instruments using part Texas Instruments TMS9900

Instrument Manufacturer Class Model Description Introduced
7854 Tektronix Oscilloscope 7854 400 MHz waveform-processing scope 1980

Supported by

See also Microprocessor support table