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).
200.000 Issue 1 23-Feb-1979 [0] Note there is an error on this version: NWDS and NRDS are swapped at pins 3 & 8 of IC12
Documentation:
Refer to the System 1 Technical Manual
Photos:
200.000 Issue 3 #1 [0]
200.000 Issue 3 #2 [3 System 4]
200.000 Issue 3 #3 [3 System 4]
200.000 Issue 3 #4 [3 System 4]
Data Sheets:
Replica Board: