The Apple ImageWriter I dot-matrix printer used a 25-pin D-sub (DB-25) RS-232-style serial connector for communication with the host computer. The later ImageWriter II, introduced in 1985, replaced this with an 8-pin mini-DIN (DIN-8) RS-422 serial connector compatible with the Macintosh Plus and subsequent Mac serial ports. Both variants carry serial data signals, though the DIN-8 model operates on balanced RS-422 differential pairs rather than RS-232 voltage levels.
25 pin D-SUB male connector
25 pin D-SUB female connector
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | GND | - | Ground |
| 2 | SD | OUT | Send Data |
| 3 | RD | IN | Receive Data |
| 4 | RTS | OUT | Request To Send |
| 7 | GND | - | Ground |
| 14 | FAULT- | OUT | False when deselected |
| 20 | DTR | IN | Data Terminal Ready |
Notes
- Direction is Printer relative to Computer.
- The DB-25 connector shown here applies to the original ImageWriter I.
- The ImageWriter II uses an 8-pin mini-DIN (DIN-8) connector carrying RS-422 balanced differential serial signals, compatible with the Macintosh Plus and later Macintosh serial ports.
- The Apple System Peripheral-8 cable (M0187, assembly 590-0340-A) connects a Macintosh Plus or later serial port (DIN-8) directly to the ImageWriter II, with pins cross-wired: 1↔2, 3↔5, 6↔8, with pins 4 and 7 straight through.
Signals
- GND — Signal ground; pins 1 and 7 are both chassis/signal ground returns.
- SD — Send Data; serial data transmitted from the printer to the host.
- RD — Receive Data; serial data received by the printer from the host.
- RTS — Request To Send; flow-control output from the printer.
- FAULT- — Printer fault indicator; asserts false (low) when the printer is deselected or in a fault condition.
- DTR — Data Terminal Ready; input from the host indicating readiness to communicate.