Macintosh to PC Null Modem Cable Pinout
From AllPinouts
Cable pinout for: Macintosh to PC Null Modem
This cable allows you to connect a Macintosh to a PC through the serial port.
"It worked perfectly, allowing me to do PPP and regular serial connections from the mac to the PC (which happened to be running Linux)."

8 Pin DIN Male Macintosh connector (to Macintosh computer)

25 PIN D-SUB Female (to PC serial port)

9 PIN D-SUB Female (to PC serial port)
| Macintosh Signal Description | Mac DIN 8 Male | PC DB 25 Female | PC DB 9 Female |
|---|---|---|---|
| HSKo (Output Handshake) | 1 (OUT) | 5, 6, 8 (CTS, DSR, DCD) | 8, 6, 1 (CTS, DSR, DCD) |
| HSKi (Input Handshake) | 2 (IN) | 4 (RTS) | 7 (RTS) |
| TxD- (Transmit Data -) | 3 (OUT) | 3 (RxD) | 2 (RxD) |
| GND (Signal Ground) | 4 (GND) | 7 (GND) | 5 (GND) |
| RxD- (Receive Data -) | 5 (IN) | 2 (TxD) | 3 (TxD) |
| TxD+ (Transmit Data +) | 6 (OUT) | - | - |
| GPi (General Purpose Input) | 7 (IN) | 20 (DTR) | 4 (DTR) |
| RxD+ (Receive Data +) | 8 (IN, GND = RS232 Mode) | 7 (GND) | 5 (GND) |
