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:
For 6502 CPU Board clocked at 1MHz fit links LK6 and LK12
For 6502A CPU Board clocked at 1MHz fit links LK6 and LK13
For 6502A CPU Board clocked at 2MHz fit links LK6 and LK13
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 |
| LK8A,B | ||
| LK9A,B | ||
| LK10A,B | ||
| LK11A,B | ||
| 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.
Schematic
Bill Of Materials
Front Panel Drilling
Blank PCB
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