6502 Microcomputer

The core of the System range of computers available as either a Microcontroller (left) or Microcomputer (right). 

"This Acorn single board microcontroller was designed for low cost industrial applications and is based on the 6502 processor. It is a Eurocard (100 x 160mm) made of a high quality glass fibre laminate with through hole plating solder resist and component identification. The standard controller is provided with 6502, 128 bytes of RAM, 16 lines of I/O, capacitor controlled clock and address decoding and logic. This board also has provision for up to 4½Kbytes of ROM (32 + 2 of 74S571), 1¼K bytes of RAM (2114) and 32 lines of I/O (2 x 8154), a crystal controlled clock is also optional. The processor used employs pipelining giving fast execution times (4µs for load accumulator, 6 µs for jump to sub-routine and 2 µs for internal register operations). It is noted for its wide range of powerful addressing modes and harmonious instruction set.

The I/O device used is the INS8154 whose sixteen lines are single bit addressable, can be individually configured and are TTL compatible. A handshake mode is provided facilitating asynchronous data transfer at high speed, and direct interface to peripherals. A wide variety of memory - I/O configurations can be selected by wire links in the address select socket on board.

The standard Eurocard edge connector carries the address and data bus, eight control lines, sixteen I/O lines, the single DC supply rail and 5v regulated output from the onboard regulator. The opposite end of the card has 16 1/0 lines, two control lines and 5v output."

"The 6502 Microcomputer is designed for use in the Acorn Systems 2, 3, and 4 and it plugs on to the standard Acorn 8 or 14 slot backplanes. The 6502 microprocessor is run from a 1MHz crystal controlled clock and for TTL devices provides address decoding.

On the card is 1K byte of static RAM in 2114's and an 8154 1/0 device provides 16 I/O lines, 8 of which connect to an ASCI I keyboard via a 20-way ribbon cable connector. Other lines on the 8154 can connect to the cassette interface via the backplane.

A second 8145 can be fitted giving 16 other I/O lines on the 64-way connector and a ROM can also be added to carry the systems OS software (alternatively this can be on a static RAM card)."

Schematic (200.000 Issue 1 23-Feb-1979) Note there is an error on this version: NWDS and NRDS are swapped at pins 3 & 8 of IC12

Schematic (100.000 Issue 3 1980)

Data Sheets:






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