50 pin Mac Internal
ROM Expansion Connector
Due to the unique nature of the Macintosh Portable, developers now have the ability to add ROM to the Macintosh. To provide for compatible shared use of this ROM space with Apple and other developers.
| Pin | Signal | Description |
|---|---|---|
| 1 | +5V | Vcc |
| 2-24 | A1-A23 | Unbuffered 68HC000 address signals A1-A23 |
| 25-26 | GND | Logic Ground |
| 27 | /DTACK | /DTACK input to 68HC000 |
| 28 | /AS | 68HC000 address strobe signal |
| 29 | /ROM_CS | Permanent ROM chip select signal. Selects in range $90 0000 through $9F FFFF |
| 30 | 16MHz_Clock | 16 MHz system Clock |
| 31 | /EXT_DTACK | External /DTACK signal that disables main system /DTACK |
| 32 | /DELAY_CS | This signal is generated by the addressing PAL and is used to put the ROM board into the idle mode by inserting multiple wait states |
| 33-48 | D0-15 | 68HC000 unbuffered data signals D0-15 |
| 49-50 | +5V | Vcc |
References
- Macintosh Portable ROM Expansion (pdf link)
- Inside Macintosh, Volume II, IV, & V, The Disk Driver