9 pin D-SUB male connector
9 pin D-SUB female connector
The Apple LaserWriter’s RS-422 serial port uses a 9-pin D-sub (DB-9) connector carrying balanced differential data pairs (TxD+/TxD− and RxD+/RxD−) in accordance with EIA-422-A. This interface provides the AppleTalk/LocalTalk connection between an original Macintosh (128K or 512K) and a LaserWriter printer, operating at the LocalTalk data rate of 230.4 kbit/s. The Zilog Z8530 Serial Communications Controller drives both data and clock lines; the TRxC output on pin 7 supplies the receive clock to the peripheral. Direction is given relative to the computer.
| Pin | Name | Dir | Description |
|---|---|---|---|
| 1 | GND | - | Ground |
| 2 | n/c | Not connected | |
| 3 | GND | - | Ground |
| 4 | TXD+ | OUT | Transmit Data + |
| 5 | TXD- | OUT | Transmit Data - |
| 6 | n/c | Not connected | |
| 7 | RXCLK | OUT | TRxC of Zilog 8530 |
| 8 | RXD+ | IN | Receive Data + |
| 9 | RXD- | IN | Receive Data - |
Signals
- GND — Signal ground; pins 1 and 3 are both grounded.
- n/c — Not connected; pins 2 and 6 carry no signal on this cable.
- TXD+ — Transmit Data positive (non-inverting); part of the RS-422 differential transmit pair.
- TXD- — Transmit Data negative (inverting); part of the RS-422 differential transmit pair.
- RXCLK — Receive clock output; driven by the TRxC output of the Zilog Z8530 SCC on the computer side.
- RXD+ — Receive Data positive (non-inverting); part of the RS-422 differential receive pair.
- RXD- — Receive Data negative (inverting); part of the RS-422 differential receive pair.
Notes
- Direction is given relative to the computer.
- Signalling conforms to EIA-422-A (balanced differential); the data pairs are not RS-232 compatible.
- This DB-9 connector was used on the original Macintosh 128K and 512K. From the Macintosh Plus (1986) onward, Apple replaced the DB-9 with an 8-pin mini-DIN (DIN-8) serial connector carrying the same RS-422 signals.
- The LaserWriter also provides a DB-25 RS-232C port for point-to-point connection from non-Apple hosts; a mode switch on the printer selects between the RS-422 AppleTalk interface and the RS-232C interface.
- LocalTalk network segments support a maximum of 32 devices and a maximum span of 300 metres.