AMD Am2900

Am2900 is a family of integrated circuits (ICs) created in 1975 by Advanced Micro Devices (AMD). They were constructed with bipolar devices, in a bit-slice topology, and were designed to be used as modular components each representing a different aspect of a computer control unit (CCU). By using the bit slicing technique, the Am2900 family was able to implement a CCU with data, addresses, and instructions to be any multiple of 4 bits by multiplying the number of ICs. This requires more ICs to implement than what could be done on a single CPU IC, but at the time, the TTL Am2900 chips ran at 20–40Mhz, which was much faster than the 2–3Mhz CMOS/NMOS microprocessors of the era such as the Intel 8085. 8085 emulators were implemented around two Am2900 chips which ran 5 to 10 times faster than the 8085-based designs they replaced.

The Am2901 chip included an arithmetic logic unit (ALU) and 16 4-bit processor register slices, and was the "core" of the series. It could count using 4 bits and implement binary operations as well as various bit-shifting operations. The Am2909 was a 4-bit-slice address sequencer that could generate 4-bit addresses on a single chip, and by using n of them, it was able to generate 4n-bit addresses. It had a stack that could store a microprogram counter up to 4 nest levels, as well as a stack pointer.

The 2901 and some other chips in the family were second sourced by an unusually large number of other manufacturers, starting with Motorola and then Raytheon – both in 1975 – and also Cypress Semiconductor, National Semiconductor, NEC, Thomson, and Signetics. In the Soviet Union and later Russia the Am2900 family was manufactured as the 1804 series (with e.g. the Am2901 designated as KR1804VS1 / Russian: КР1804ВС1) which was known to be in production in 2016.