Connector 1
Connector 2
Function
2 3 Rx <------- Tx
3 2 Tx --------> Rx
5 5 Signal ground

Connector 1 represents the DB9 connector pins for the computer's serial port.
Connector 2 represents the pins on the S12 receiver.
Only three pins are needed to make the RS232 connector work.
The diagram shown above got the RS232 working on my S12. EB