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Acorn 1MHZ 6502 CPU

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Acorn 1MHz 6502 CPU card

Acorn 1MHZ 6502 CPU card (front) 

Acorn 1MHz 6501 CPU card back

Acorn 1MHz 6502 CPU card (back) 

An Acorn 1MHz 6502 CPU card from a System 1 (see the 4 rubber feet on the bottom). The part number is 200,000 issue 3. The card has a Rockwell 6502 with INS8154 devices at either end controlling I/O to the keyboard and dispay card (on left) and the Eurocard connector (on the right). Next to the 6502 CPU are the 2 x 2114 RAM ICs giving 1K RAM and the 2 x 74S571 ROMs ( with blue and yellowspots) giving 512bytes ROM. The large empty socket is for a 2516 UV PROM. The power connector is on the right hand side.
The 6502 card can also be used as the CPU in a System 2, 3 or 4 connecting to the chassis using the Eurocard connector on the right hand side.

Acorn 1MHz 6502 CPU front

 Acorn 1MHZ 6502 CPU card (front) 

Acorn 1MHz 6502 CPU back

 Acorn 1MHZ 6502 CPU card (front) 

This Acorn 1MHz 6502 CPU card is from a System 4. The part no. is 200,000 Issue 3. The ROMs in IC5/6 are missing as the monitor is not needed and IC7 which can hold an OS ROM is empty. The second INS8154 RAM IO is not installed.

The 6502 card is designed for use in the Acorn system 2, 3 and 4 and it plugs into the standard Acorn 8 or 14 slot backplanes. The 6502 microprocessor is run from a 1MHz crystal controlled clock and a TTL device provides address decoding.

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

A second 8154 can be fitted giving a further 16 I/O lines on the 64-way connector and a ROM can be added to carry the Operating System software. (Alternatively this can be on a static RAM card).