Replica 80x25 VDU Interface Board 

Replica 80x25 VDU Interface Board Photo

Based on the issue 4 schematic and photos of an Issue 4 board.

Presets RV1 and RV2 are adjusted to get a 12MHz and 2MHz clock respectively (if the local oscillators are used).

Links LK7, 8, 9, 10 and 11 are normally fitted in position A to select addresses as used by Acorn System COS and DOS.

Links LK4, 5, 6, 12 and 13 depend on which CPU Board is being used:

Link Summary:

LK1 Light Pen Normally not fitted
LK2 Invert Cursor Normally not fitted
LK3 VMA Normally fitted
LK4 2MHz (LO) Fit to use Local Oscillator derived 2MHz clock
LK5 2MHz (O2) Fit to use O2 as 2MHz clock
LK6 2MHz (Bus) Fit to use Bus derived 2MHz clock
LK7A,B Address Select Links normally fitted in 'A' positions for $1840-187F, fit in 'B' positions for E840-E87F
LK12 12MHz (LO) Fit to use Local Oscillator derived 12MHz clock
LK13 12MHz (Bus) Fit to use Bus derived 12MHz clock

You may find you need to adjust the value of R8 to get good results, the original Acorn board used 150R but I have found that 100R works better.  Also Acorn originally specified 200nS 2114 RAM chips, I have boards working with 200 and 300nS access times but have reports that 150nS are required so you may need a bit of experimenting to get best results.


Bill Of Materials

Front Panel Drilling

Blank PCB

Replica 80x25 VDU Interface Board PCB


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