MK4118 SRAM 1K x 8 pinout
DIP-24. Static RAM: the single-chip 1 KB option of the ZX81
1K x 8 static RAM in 24 pins on +5 V alone (Mostek MK4118). One chip gives the ZX81 its 1 KB. Pin 19 is a latch input: tied HIGH it makes the chip a plain static RAM. A 2K x 8 6116 has A10 on pin 19, so it is not a direct swap unless pin 19 is held at the level the board expects. A bad 4118 gives garbage on the screen or a crash. ZX81: IC4 takes it in place of the two 2114s IC4a and IC4b, and the wire link L1 must be fitted with it (ZX81 Service and Assembly Manual).
Open the interactive 4118 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | A7 | addr | Address bit 7. |
| 2 | A6 | addr | Address bit 6. |
| 3 | A5 | addr | Address bit 5. |
| 4 | A4 | addr | Address bit 4. |
| 5 | A3 | addr | Address bit 3. |
| 6 | A2 | addr | Address bit 2. |
| 7 | A1 | addr | Address bit 1. |
| 8 | A0 | addr | Address bit 0. |
| 9 | DQ0 | data | Data in/out 0. |
| 10 | DQ1 | data | Data in/out 1. |
| 11 | DQ2 | data | Data in/out 2. |
| 12 | VSS | ground | 0 V. |
| 13 | DQ3 | data | Data in/out 3. |
| 14 | DQ4 | data | Data in/out 4. |
| 15 | DQ5 | data | Data in/out 5. |
| 16 | DQ6 | data | Data in/out 6. |
| 17 | DQ7 | data | Data in/out 7. |
| 18 | /CE | ctrl | Chip enable, active LOW. |
| 19 | /L | ctrl | Latch: LOW latches the address and /CE; tie HIGH for plain static operation. |
| 20 | /OE | ctrl | Output enable, active LOW. |
| 21 | /WE | ctrl | Write enable. LOW writes the data pins. |
| 22 | A9 | addr | Address bit 9. |
| 23 | A8 | addr | Address bit 8. |
| 24 | VCC | power | +5 V supply. |
Fitted in
- ZX81 IC4, the 24-pin option in place of the 2114 pair