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:

No other links need to be fitted for normal use.

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.

Schematic

Bill Of Materials

Front Panel Drilling

Blank PCB

Replica 80x25 VDU Interface Board PCB

 

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