There are 4 expansion slots on the board.
Each slot is using a 64-pin DIN 41612 connector. The connector supply data, address and some common bus signals as well as power to each of the boards.
There are also 2 select signals for each slot, all access for each slot is memory mapped on on the address bus.
One is a 256-byte range that is designed for register access or control and a 1-Megabyte range for accessing data. For example, on the VGA card the control of the card if done through the registers, but if needed direct access to the VRAM can be done through the data range.
The signals for the expansion slot are:
- Power supplies available are +5V, +3.3V, +12V -12V, GND and a +5V Standby voltage from the ATX power supply.
- D0 to D15 data lines.
- A1 to A19 address lines.
- Slot select signals CS_REG and CS_DATA.
- 68000 Bus signals AS, LDS, UDS, R/W, RESET, VMA, VPA and E.
- CPU clock.
- Presence detect signal, pulled low when board is connected to bus.
- Bus response signals.
- IRQ - Active low interrupt for each slot (1-3, no interrupt on slot 4).
- DTACK - Active low acknowledge for bus access.
- BERR - Bus error can be generated for illegal access.