AMD Am2900

Lore & Background

The Am2900 family was created in 1975 by Advanced Micro Devices using bipolar devices in a bit-slice topology. By using the bit slicing technique, the family could implement a control unit with data, addresses, and instructions to be any multiple of four bits by multiplying the number of ICs. This required more ICs than a single CPU chip, but the TTL Am2900 chips ran at 20–40 MHz, much faster than the 2–3 MHz CMOS/NMOS microprocessors of the era such as the Intel 8085. Emulators of the 8085 were implemented around two Am2900 chips and ran 5 to 10 times faster than the 8085-based designs they replaced.

The Am2901 chip included an arithmetic logic unit 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 could generate 4n-bit addresses. It had a stack that could store a microprogram counter up to four nest levels, as well as a stack pointer.

The Am2901 and some other chips in the family were second sourced by an unusually large number of other manufacturers, starting with Motorola and Raytheon 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 the Am2901 designated as KR1804VS1, known to be in production in 2016.

Reader's Guide

The Am2900 family's significance lies in its bit-slice architecture, which allowed designers to build processors with arbitrary word widths by cascading 4-bit slices, achieving performance far exceeding contemporary single-chip microprocessors. This flexibility made it a popular choice for minicomputers, floating-point units, and specialized controllers throughout the late 1970s and 1980s. The family was used in a wide range of machines, including the DEC PDP-11 and VAX 11/730, the Data General Nova 4, the Hewlett-Packard 1000 A-series, the Xerox Dandelion, the GEC 4000 series, the DEC KS10 (PDP-10), the Lilith computer, Atari's vector and raster graphics arcade machines, the Pixar Image Computer, the Eventide H949 Harmonizer, the AT&T 3B20D, the Geac Computer Corporation models, the Ferranti Argus 700, the High Level Hardware Limited Orion, the SLAC 168/E, the Warrex Centurion, the PerkinElmer 3200 series, the NCR I-8250 family, the Chyron IV character generator, and the Prime Computer P300. The family's longevity is evidenced by its continued production in Russia as the 1804 series into 2016.

Did You Know?

• The Am2901 was second sourced by an unusually large number of manufacturers, including Motorola, Raytheon, Cypress Semiconductor, National Semiconductor, NEC, Thomson, and Signetics.
• The Am2900 family was used in Atari's vector graphics arcade machines Red Baron, Battlezone, and Tempest, each using four Am2901 ICs in their math box auxiliary circuit boards.
• The Soviet Union and later Russia manufactured the Am2900 family as the 1804 series, with the Am2901 designated as KR1804VS1, still in production as of 2016.
• The DEC VAX 11/730 used eight Am2901s in its CPU.