Looking at the connector on the back of the computer, the pins are numbered: 5 1 4 2 3 The functions are: 1 DTR (flow control out) 2 TxD (data out) 3 Ground 4 RxD (data in) 5 DSR (flow control in) ---------------------------------------------------------------- From IIc Reference Manual Vol I 5. .1 4. .2 1. Port 2 1 - DTR2B - Data Terminal Ready output 2 - TD2B - Transmit Data Output 3 - GND - Ground 4 - RD2B - Read Data Input 5 - DSR2B - Data Set Ready Input If you are building the cable for a normal 2400 modem, stright through will work. for High speed here what the ProTerm manual says. Computer Modem 2 -> 2 TD 4 -> 3 RD 3 -> 7 GND 5 -> 6 DSR 1 -> 4 RTS Short 4 to 20 DTR