Texas Instruments SBP0400

The Texas Instruments SBP0400 (SBP = silicon bipolar), also known as SBC 0400 and X0400, is a microprogrammable 4-bit slice processor that was introduced in 1976 (delivery began in December 1975).

[1] It was one of the first LSI processors and was the first device in the USA based on I²L technology (integrated injection logic).

[2] It was used for research and teaching purposes in the aerospace industry (NASA)[2] and in the learning computer LCM-1001 (Texas Instruments, 1976).

The control switches are: ALUCIN (ripple-carry in), PCPRI (program counter priority, required to turn on the output LEDs on the address bus, PCCIN (program counter carry-in), ENCBY2 (enable program counter increment by a displacement of 1 or 2), POS1, POS0 (most significant, intermediate, or least significant position of the processor slice in a cascade).

The 74S481 was used to implement TI's 990/12 minicomputer, where it combined ROM with writable control store.