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Compax3 will not communicate via RS232 serial or with C3 ServoManager

General video showing how to troubleshoot a PC and RS232 communication:
Read below for further items to check


If you are unable to communicate RS232 with your Compax3 using the C3 ServoManager, please check the following:

1) If not using the Parker green serial cable SSK1/02, make sure pin1 is not connected to the PC. If it is, the Compax3 will autodetect in rs485 mode. Remove pin1 with snips and cycle power on the +24vdc on the Compax3. Then connect the cable to the Compax3.  For details see item 10 below.

2) Is the RS232 cable connected to the correct COM port on the PC? Is the RS232 cable connected to X10 on the Compax3?

3) Are you trying to use RS485 communication with the C3 ServoManager? The C3 ServoManager must use RS232 communication only. Are you trying to connect at a different baud rate other than 115200? The RS232 communication on the Compax3 is fixed at 115200.

4) Is the COM port properly configured in the C3 ServoManager? To verify that the correct COM port (the port on your PC) is chosen, please go to the Options pulldown menu in C3 ServoManager. Select the COM Port(RS232/RS485).., and verify the COM Port setting is the port you want to use.

5) Is a 24VDC supply connected to X4 on the Compax3. Is the 24VDC powered? To communicate, an external 24VDC supply must be provided and wired to to X4/1 and X4/2 on the Compax3. Are the LED's illuminated (on or blinking, red or green) on the front of the unit? If the Compax3 is only supplied the AC Mains voltage (AC voltage to connector X1) the LED's will NOT illuminate and communication is not possible.

6) Is the RS232 cable wired properly? The recommended cable pinout can be found in the Interface Cable section of the Compax3 User Guide. The cable part number is SSK1/.. However, only 3 wires are required for communication - Tx, Rx, and GND (Ground). Therefore, successful communication is possible, but the additional connections add robustness to the communication.

7) Is the COM port available or does another resource have the COM? Please verify no other programs on the PC are using the COM port that the C3 ServoManager is trying to use. You can verify the COM port setting in the C3 ServoManager by referring to item 3 in this FAQ.
Also, only one resource within C3 ServoManager can be using the COM port. Either the IEC Debugger Tool, the IEC Logic Analyzer (within the Debugger), or the Optimization Tool (includes the O-Scope and Status Display) can be active (scanning the drive)at one time, however, all three may be open on your PC.

8) Are you using a USB to Serial Port adapter? 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** (available on This adapter has the FTDI chipset.

Previously recommended was BAFO BF-800 (25-pin RS232 version) and the BF-810 (9-pin RS232 version) which does work on Win XP and prior but the drivers do not work on Windows 7 (Win7). This adapter has the Prolific chipset.

Specifically the Keyspan USA-19HS does not work with C3 ServoManager software.

This adapter gives a 9pin com port output; a null modem crossover cable is still necessary to connect from the adapter to the Compax3.**

9) Set up HyperTerminal for a Baud Rate of 115,200 with 8 bits, 1 stop bit, and no Parity. You won't be able to see what you type or any prompt. Hit , they type "o680.5" (where the first digit is a lower-case "oh") and hit again. This will return position information. By turning the motor, you can change this. If a !FF or similar response is returned, the Compax3 didn't like the command.

10) Are you using an industry standard Null Modem cable provided by a non-Parker supplier? 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 industrystandard 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. The industry standard Null Modem connection is as follows:

For more information on Null Modem Cables click here
Signal Name DB-25 Pin DB-9 Pin DB-9 Pin DB-25 Pin
FG (Frame Ground) 1 - X - 1 FG
TD (Transmit Data) 2 3 - 2 3 RD
RD (Receive Data) 3 2 - 3 2 TD
RTS (Request To Send) 4 7 - 8 5 CTS
CTS (Clear To Send) 5 8 - 7 4 RTS
SG (Signal Ground) 7 5 - 5 7 SG
DSR (Data Set Ready) 6 6 - 4 20 DTR
CD (Carrier Detect) 8 1 - 4 20 DTR
DTR (Data Terminal Ready) 20 4 - 1 8 CD
DTR (Data Terminal Ready) 20 4 - 6 6 DSR

Also, the standard gender of the Null Modem cable 9 Pin D-Sub connector is female on both ends. The Compax3 requires a male 9 Pin D-Sub connector for X10, the RS232 port.Since a 9 Pin D-Sub male to male adapter must be used with a standard null modem cable, a quick solution is to cut pin 1 of the male 9 Pin D-Sub adapter on the side that plugs into the Compax3.**

**Note:'s ICUSB232FTN provides a USB to RS232 adapter null modem output.  This includes the FTDI chipset and has Tx and Rx indicator LEDs. This is a Null Modem output and saves the cost of a null modem cable. As this has a female output, a DB9 male/male gender changer adapter would fit this to the Compax3.  However, use a small flathead screw-driver and break pin 1 off to prevent the Compax3 powering in RS485 mode. Both the ICUSB232FTN and GC9SM items are available on and their Prime service.


11) Does your PC's operating system and hardware meet the minimum requirements listed in the Commissioning Compax3 chapter of the User Guide?