RS Logix Lock-Up on Micrologix 1000

[Rockford 0]

I have an application with an extremely simple program running in a Micrologix 1000 PLC. When I activate any of the inputs on the processor the RS Logix looses communication with the processor and gives the "Offline" or "Retry" message. The only way the PLC will reestablish communication with the PC is by restarting the PC, RS Linx and RS Logix. The PC works on other PLC's on other machines without problems and the USB ports on the PC appear to be functioning normally with other USB devices. When this problem occurs the PLC doesn't fault or stop working as the machine continues to function, just the PC communications lock up. Corrective actions taken: Replaced PLC - no effect, same results Turned off Autobrowse on RS Logix - no effect, same results (Saw this idea in another thread on this site.) I have seen RS Logix do some strange things with serial/USB ports, but I have never seen this situation. Please post any suggestions to fix this problem and I will gladly try them. Thank you.

[Mickey 71]

Check and double check grounding to the PLC. Try using the laptop running on battery power only. ( this is a grounding issue)

[Ken Roach 194]

I agree strongly; there's noise coming into the controller via those I/O circuits and it's passing up through the common wire on the RS-232 port. Make sure you have a Big Fat Green Wire for grounding the MicroLogix, and I agree that sometimes just running the PC on battery power will resolve a ground potential difference issue. Otherwise an isolator on the serial port will do the job. USB/USB, or RS232/RS232, or an isolated RS-232/USB interface. B&B Electronics makes the very best in the business.