The Spectravideo SVI-318 and SVI-328 are 8-bit home computers introduced in 1983 by Spectravideo International Ltd., built around the Zilog Z80A CPU running at approximately 3.58 MHz. Their expansion port — marketed as the Super Expander port — is a 50-pin male edge connector on the rear of the computer that exposes the full Z80 bus to peripheral cards. The connector carries a buffered 16-bit address bus, an 8-bit bidirectional data bus, all Z80 control signals, a 3.58 MHz clock output, three power rails, and a set of memory-bank control lines that allow expansion hardware to bank-switch or disable on-board RAM and ROM. Two dedicated signals (EXCSR and EXCSW) and an audio mixing input (CSOUND) support the SVI-603 Coleco game adapter.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | +5v | OUT | Power, 300mA |
| 2 | /CNTRL2 | IN | Game adapter control signal |
| 3 | +12v | OUT | Power, 100mA |
| 4 | -12v | OUT | Power, 50mA |
| 5 | /CNTRL1 | IN | Game adapter control signal |
| 6 | /WAIT | IN | Z80 WAIT |
| 7 | /RST | IN | Z80 RST |
| 8 | CPU CLK | OUT | Buffered 3.58MHz system clock |
| 9 | A15 | OUT | Buffered Address bus |
| 10 | A14 | OUT | " |
| 11 | A13 | OUT | " |
| 12 | A12 | OUT | " |
| 13 | A11 | OUT | " |
| 14 | A10 | OUT | " |
| 15 | A9 | OUT | " |
| 16 | A8 | OUT | " |
| 17 | A7 | OUT | " |
| 18 | A6 | OUT | " |
| 19 | A5 | OUT | " |
| 20 | A4 | OUT | " |
| 21 | A3 | OUT | " |
| 22 | A2 | OUT | " |
| 23 | A1 | OUT | " |
| 24 | A0 | OUT | " |
| 25 | /RFSH | OUT | RAM expansion refresh |
| 26 | /EXCSR | IN | Video-CPU write select |
| 27 | /M1 | OUT | Z80 M1 |
| 28 | /EXCSW | IN | CPU-Video write select |
| 29 | /WR | OUT | Z80 WR |
| 30 | /MREQ | OUT | Z80 MREQ |
| 31 | /IORQ | OUT | Z80 IORQ |
| 32 | /RD | OUT | Z80 RD |
| 33 | D0 | I/O | Buffered Data Bus |
| 34 | D1 | I/O | " |
| 35 | D2 | I/O | " |
| 36 | D3 | I/O | " |
| 37 | D4 | I/O | " |
| 38 | D5 | I/O | " |
| 39 | D6 | I/O | " |
| 40 | D7 | I/O | " |
| 41 | CSOUND | IN | Audio input signal |
| 42 | /INT | IN | Z80 INT |
| 43 | /RAMDIS | IN | Disable user RAM |
| 44 | /ROMDIS | IN | Disable basic ROM |
| 45 | /BK32 | OUT | Enable bank 32 Memory (8000-ffff) |
| 46 | /BK31 | OUT | Enable bank 31 Memory (0000-7FFF) |
| 47 | /BK22 | OUT | Enable bank 22 Memory (8000-FFFF) |
| 48 | /BK21 | OUT | Enable bank 21 Memory (0000-7FFF) |
| 49 | GND | - | System Ground |
| 50 | GND | - | System Ground |
Notes
The expansion port is a 50-pin male edge connector mounted on the rear of the computer. Total power available to all peripheral cards combined is limited to +5 V/300 mA, +12 V/100 mA, and −12 V/50 mA. All address and data lines are buffered; the data bus is bidirectional. Active-low signals are indicated by a leading slash (/).
Signals
- +5V — +5 V power rail; 300 mA maximum for all peripheral cards combined.
- +12V — +12 V power rail; 100 mA maximum.
- −12V — −12 V power rail; 50 mA maximum.
- GND — system ground (pins 49 and 50).
- CPU CLK — buffered 3.58 MHz Z80 system clock output.
- A0–A15 — buffered 16-bit address bus output from the Z80A (pins 9–24, A15 to A0).
- D0–D7 — buffered 8-bit bidirectional data bus (pins 33–40).
- /MREQ — Z80 memory request; active low.
- /IORQ — Z80 I/O request; active low.
- /RD — Z80 read strobe; active low.
- /WR — Z80 write strobe; active low.
- /M1 — Z80 machine cycle 1 (op-code fetch); active low.
- /RFSH — Z80 DRAM refresh cycle indicator; used by RAM expansion cards.
- /WAIT — Z80 WAIT input; peripheral cards pull low to insert wait states.
- /RST — Z80 RESET input; active low.
- /INT — Z80 maskable interrupt request; active low.
- /CNTRL1, /CNTRL2 — game adapter control signal inputs; used by the SVI-603 Coleco adapter.
- /EXCSR — external CPU-from-VDP read select; used by the Spectravideo game adapter to redirect VDP reads for Coleco cartridge compatibility.
- /EXCSW — external CPU-to-VDP write select; used by the Spectravideo game adapter to redirect VDP writes for Coleco cartridge compatibility.
- CSOUND — audio mixing input from the Spectravideo game adapter; mixed into the computer’s audio output.
- /RAMDIS — pulling this line low disables the on-board user RAM, allowing an expansion card to substitute its own RAM.
- /ROMDIS — pulling this line low disables the on-board BASIC ROM, allowing expansion ROM to take its place.
- /BK21, /BK22 — memory bank control outputs for the lower 32 K blocks (0000H–7FFFH); pulling low enables the respective bank.
- /BK31, /BK32 — memory bank control outputs for the upper 32 K blocks (8000H–FFFFH); pulling low enables the respective bank.