ZX81 8K BASIC ROM (2364 type) pinout
DIP-24. BASIC, editor, character set and floating point at $0000-$1FFF
An 8K mask ROM in the 24-pin 2364 pinout, selected on pin 20. Board wiring (ZX81 circuit diagram SRC 049; the TS1000 board follows it): /ROMCS comes from ULA pin 13 through R28 (680 ohm), and an add-on can pull it HIGH from edge pin B23 to switch the ROM out; A0-A8 come from the ULA side of the 1 kohm resistors, so the ULA can fetch character patterns while the CPU is busy. The TS1500 wiring is not confirmed. A dead ROM gives a blank or garbage screen.
Open the interactive ROM pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | A7' | addr | Address bit 7, from the ULA side (A7'). |
| 2 | A6' | addr | Address bit 6 (A6'). |
| 3 | A5' | addr | Address bit 5 (A5'). |
| 4 | A4' | addr | Address bit 4 (A4'). |
| 5 | A3' | addr | Address bit 3 (A3'). |
| 6 | A2' | addr | Address bit 2 (A2'). |
| 7 | A1' | addr | Address bit 1 (A1'). |
| 8 | A0' | addr | Address bit 0 (A0'). |
| 9 | D0 | data | Data out bit 0 (drawn D0' on the diagram). |
| 10 | D1 | data | Data out bit 1 (drawn D1' on the diagram). |
| 11 | D2 | data | Data out bit 2 (drawn D2' on the diagram). |
| 12 | 0V | ground | 0 V. |
| 13 | D3 | data | Data out bit 3. |
| 14 | D4 | data | Data out bit 4. |
| 15 | D5 | data | Data out bit 5. |
| 16 | D6 | data | Data out bit 6. |
| 17 | D7 | data | Data out bit 7. |
| 18 | A11 | addr | Address bit 11 (direct from the CPU). |
| 19 | A10 | addr | Address bit 10 (direct). |
| 20 | /ROMCS | ctrl | Chip select, active LOW (board wiring: see the summary). |
| 21 | A12 | addr | Address bit 12 (direct). |
| 22 | A9 | addr | Address bit 9 (direct). |
| 23 | A8' | addr | Address bit 8 (A8', ULA side). |
| 24 | +5V | power | +5 V supply. |
