Applicable Systems
GP4000 Series
Symptoms
Screen shows 'PLC No Response' and all animated values freeze at last known state.
Possible Causes
- Serial RS-422 cable disconnected or terminating resistor missing on the PLC side.
- Baud rate mismatch between GP4000 COM1 port and PLC serial port settings.
- PLC switched to STOP mode or watchdog error causing it to cease data updates.
Troubleshooting Steps
- Step 1: Check the RS-422 cable continuity and confirm 110 Ohm termination at the PLC.
Cable passes continuity test and termination resistor is present. - Step 2: Open GP-Pro EX, verify COM1 baud rate, data bits, parity, and stop bits.
Settings exactly match the PLC programming software port configuration. - Step 3: Monitor the PLC RUN/STOP LED and check error flags in the PLC diagnostic buffer.
PLC is in RUN mode and no critical errors are logged in the diagnostic buffer.
How to Reset
Restore the serial cable and termination, match baud settings, and return the PLC to RUN mode.
Common Replacement Parts
- RS-422 termination resistor 110 Ohm: RS-422 termination resistor 110 Ohm
Source: Pro-face GP4000 Series Connection Manual
Category: HMI