|2||HSKi/Clock||Input handshake or external clock|
|3||TxD-||Transmit data (minus)|
|5||RxD-||Receive data (minus)|
|6||TxD+||Transmit data (plus)|
|7||GPi||General purpose input (not on Mac+ or earlier)|
|8||RxD+||Receive data (plus)|
You'll notice these signals don't have the usual RS-232 names. This is because the Mac uses RS-422, where each signal is sent over a balanced pairs of wires, a positive (+) and a negative (-). In RS-232, the data signals are inverted; a one, marking, is minus voltage. However RS-232 control signals are not inverted. Since the TxD- signal from the Mac is inverted it can be used to drive an RS-232 receiver. Leave the TxD+ signal disconnected. Similarly, the receive data signal from RS-232 equipment is inverted, so it can drive the Mac's RxD-, but in this case the RxD+ line is grounded since the RS-422 receiver in the Mac needs valid levels on both inputs. The following page provide more in depth discussion of Macintosh serial interfacing - Macintosh Serial Port Connections, University of Utah.
The table below shows cable wiring to connect a Lucid Technologies programmer to the Mac's serial modem port. Since I don't have a Mac, any corrections or updates would be appreciated.
Mac DIN8 to Lucid DB9 programmer cable, no hardware handshake
Mac DIN8 Lucid DB9 4 (SG) 5 (SG) 8 (RxD+) 5 (SG) 5 (RxD-) 2 (RD) 3 (TxD-) 3 (TD)On the DIN8 end of the cable, connect pin-1 (HSKo) to pin-2 (HSKi). Unspecified pins on both connectors are allowed to float.
Pin Name Function 1 SG Signal ground 2 +5V 3 SG Signal ground 4 TxD+ Transmit data (plus) 5 TxD- Transmit data (minus) 6 +12V 7 CTS Clear to send 8 RxD+ Receive data (plus) 9 RxD- Receive data (minus)
Mac DB9 to Lucid DB9 programmer cable, no hardware handshake
Mac DB9 Lucid DB9 3 (SG) 5 (SG) 8 (RxD+) 5 (SG) 9 (RxD-) 2 (RD) 5 (TxD-) 3 (TD)Unspecified pins on both connectors are allowed to float.