FAQ: Autocontrol computer to Compax3 cable

How to connect Compax3 controller to PC running Autocontrol software.Parker has found that some USB to Serial adapters do not work with the C3 ServoManager. The tested (by Parker EMN) USB to Serial adapter we recommend is the Cables Unlimited part number USB-2920. This adapter has the FTDI chipset.  Specifically the Keyspan USA-19HS does not work with C3 ServoManager software.
Do not use an industry standard Null Modem cable? The problem with the standard Null Modem cable has to do with the fact that pin 1 is connected to pin 4 of the 9 Pin D-Sub connector of the cable. The Compax3 uses pin 1 of the RS232 connector, X10, to determine if the communication will be RS232 or RS485. If 5 Volts is present on pin 1 of the Compax3, it automatically switches to RS485 mode. As per the X10 pin out in the Compax3 User Guide, pin 4 is reserved for the RS232 connection. In fact, pin 4 is pulled up to a + voltage internally. Therefore, when we use the industry standard Null Modem cable, pin 1 is pulled up to a + voltage by the pin 1 to pin 4 connection in the cable, and the Compax3 is ready for RS485 communication.
RS232 computer to Compax3 X10 connector. 
Compax3 X10 to PC Wire Diagram

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