It's possible to connect RS-232 peripheral to the RS-422 port available on Macintosh computers. Use RXD- as RXD, TXD- as TXD, Ground RXD+, Leave TXD+ unconnected, GPi as CD.
(at the computer)
8 PIN MINI-DIN FEMALE at the computer.
Note: Direction is DTE (Computer) relative DCE (Modem).
Note: GPi is connected to SCC Data Carrier Detect (or to Receive/Transmit Clock if the VIA1 SYNC signal is high). Not connected on the Macintosh Plus, Classic, Classic II, LC, LC II or IIsi.