23256 mask ROM 32K x 8 pinout
DIP-28. 32K x 8 mask ROM in the 27256 pinout.
Generic pin table; the 23256 is a 27256-pinout mask ROM. CPC: the OS firmware ($0000-$3FFF lower ROM) and Locomotive BASIC ($C000-$FFFF upper ROM 0) in one 32K chip. How /CS (pin 20), /OE (pin 22) and A14 (pin 27) are driven depends on the board. CPC 464, 664 and 6128 (IC103): the Gate Array /ROMEN drives /CS; /OE is held LOW by 2.2 kΩ (R112 on the 6128) and pulled HIGH by expansion ROMDIS (pin 43) when an expansion ROM takes over. Each model has its own ROM; they are not interchangeable without the matching firmware. A 27256 EPROM needs pin 1 (VPP) at +5 V. Pin table from the CPC6128 schematic. IBM XT 5160, Portable 5155 (U18) and PCjr (XX1, ZM63): the board ties pins 1 and 27 both to A14 (XT Technical Reference 1502237 sheet 5 of 10; PCjr Technical Reference sheet 2 of 17, which draws the PCjr ROMs as MK38000).
Open the interactive 23256 pinoutPins
| Pin | Name | Type | Signal |
|---|---|---|---|
| 1 | NC | nc | Not connected (VPP on a 27256 EPROM, Microchip 27C256 data sheet p. 1). |
| 2 | A12 | addr | Address bit 12. |
| 3 | A7 | addr | Address bit 7. |
| 4 | A6 | addr | Address bit 6. |
| 5 | A5 | addr | Address bit 5. |
| 6 | A4 | addr | Address bit 4. |
| 7 | A3 | addr | Address bit 3. |
| 8 | A2 | addr | Address bit 2. |
| 9 | A1 | addr | Address bit 1. |
| 10 | A0 | addr | Address bit 0. |
| 11 | D0 | data | Data bit 0. |
| 12 | D1 | data | Data bit 1. |
| 13 | D2 | data | Data bit 2. |
| 14 | GND | ground | 0 V. |
| 15 | D3 | data | Data bit 3. |
| 16 | D4 | data | Data bit 4. |
| 17 | D5 | data | Data bit 5. |
| 18 | D6 | data | Data bit 6. |
| 19 | D7 | data | Data bit 7. |
| 20 | /CS | ctrl | Chip select. Active LOW. |
| 21 | A10 | addr | Address bit 10. |
| 22 | /OE | ctrl | Output enable, active LOW. On the CPC boards it is pulled LOW through 2.2 kΩ (R112 on the 464 and 6128) and wired to expansion ROMDIS: an expansion board can drive it HIGH to disable the ROM whatever /CS does. The outputs drive the bus only while /CS and /OE are both LOW. |
| 23 | A11 | addr | Address bit 11. |
| 24 | A9 | addr | Address bit 9. |
| 25 | A8 | addr | Address bit 8. |
| 26 | A13 | addr | Address bit 13. |
| 27 | A14 | addr | Address bit 14. |
| 28 | VCC | power | +5 V. |
Fitted in
- Amstrad CPC 464 IC103 (TMM23256P-1950; Amstrad 40009 on later boards), BASIC 1.0
- Amstrad CPC 664 IC103 (TMM23256P-1952, Amstrad 40022)
- Amstrad CPC 6128 IC103 (TMM23256P-1953; Amstrad 40025 on later boards)
- Commodore 1571 disk drive U2 (DOS 3.0, 310654-03 / -05; pin 1 VPP tied to +5 V)
- Commodore 1581 disk drive U2 (DOS 10: 312558 mask ROM or 318045 27256 EPROM; socketed)
- Apple IIc Firmware ROM marked MON (342-0033-A, a 23256 32K x 8 mask ROM on the photographed board); designator not read
- IBM XT 5160 U18, the 32K x 8 ROM (XT Technical Reference 1502237, sheet 5 of 10). 1501512 (MK38036N-25) on the photographed board
- IBM PCjr 4860 XX1 and ZM63, 32K x 8 each (PCjr Technical Reference, sheet 2 of 17, draws two MK38000). IBM 1504036 (MK38050N-25) at XX1 and 1504037 (TMM23256P) at ZM63 on the photographed board
- IBM Portable 5155 U18, the 32K x 8 ROM (as on the XT). T1501512 (TMM23256P) on the photographed board
- Acorn Electron IC2 (OS/BASIC mask ROM 201,621; LK1 sets Hitachi or Toshiba chip-select)
- MSX1 (generic) Varies by maker; the 32 KB BIOS / BASIC ROM in slot 0 (the chip-select pins differ between makers: check against the board)
Sources
- Amstrad CPC6128 / CTM644 / GT65 Service Manual, CPU circuit diagram p. 19-20, IC103 ROM
- Amstrad CPC664 Service Manual, electrical parts list (IC103 TMM-23256P-1952, part 40022)
- Amstrad CPC464 / CPC6128 / GT65 / CTM644 / MP3 Service Manual Amendment (parts lists, revised schematics)
- IBM PC XT Technical Reference 1502237 (Apr 1983), System Board sheet 5 of 10, p. D-6: U18 32K x 8 ROM, pins 1 and 27 on A14 (PDF p. 472)
- IBM PCjr Technical Reference (Nov 1983), System Board sheet 2 of 17, p. B-4: XX1 and ZM63 MK38000, pins 1 and 27 on A14 (PDF p. 502)