No Communication?
- Verify RS232/RS485 wiring matches pinout
- Confirm baud rate, parity, data bits, and stop bits match PLC settings [manualzz.com]
- Check correct COM port and driver selection
- Verify communication mode and port configuration
- Ensure PLC is powered and in RUN mode
Connection Established but No Data?
- Verify correct device prefix (X, Y, M, T, R, L, etc.) [manualzz.com]
- Confirm correct address range and format
- Check bit vs word addressing selection
- Ensure PLC program is running and updating values
Intermittent or Unstable Communication?
- Check cable condition and shielding
- Verify grounding and noise isolation
- Confirm stable power supply to PLC
- Inspect connectors and communication modules
Incorrect Data or Values?
- Verify correct register mapping and addressing
- Check byte/word interpretation
- Confirm scaling and data type
- Ensure using correct device area (input, output, memory)
Timer / Counter Issues?
- Verify correct register type for timer/counter values [manualzz.com]
- Confirm current value vs preset value usage
- Ensure PLC logic updates values correctly
Read Works but Write Fails?
- Verify register is writable
- Check PLC mode (RUN/MONITOR)
- Confirm value format and data size
- Ensure address is valid for write operations
PLC Not Responding?
- Verify PLC power and CPU status
- Check communication module configuration
- Confirm correct port selection
- Try alternate cable or communication port
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