Testing RS-422


Thread Starter


I have no real solid knowledge of this topic but have been asked to attempt to help resolve a problem. My company has purchased a blow molding machine and we cannot get the plc to talk to one of the heat controls. Can someone provide some insight into testting the rs-422 connection to be sure we even have a good connection? The manufacturer of the PLC is MOOG. I was told we have the only one in the US. Any help would be greatly appreciated.

There are a couple of things you can check for. The MOOG PLC should have some sort of receive (RX) and transmit (TX) lights. When you connect via 422, watch these lights to see if you can see a faint flicker of the PLC RX light. Regardless of parity, protocol, baud rate, or any one of the other parameters, you should see the rx light flicker in an attempt to recieve the packet.
If you see the light flicker at all, you probably have one of the afore mentioned parameter settings wrong.
If there is no light flicker at all, I would strongly suspect a cable problem. I would check the cable for continuity with an ohm-meter, correct wiring, and be sure your 422 converter is working properly..
I've had similar problems with odd-pinout cables...some that say RS-422 ain't necessarily so. I got a "break-out box" at Radio Shack, you can use jumpers to make connections. It's really helpful when you have to use trial and error to get a pinout configuration, and cheaper than having to buy new cables.