No Communication?
- Verify RS232/RS485 wiring matches pinout
- Check baud rate, parity, stop bits
- Confirm correct device address or node ID
- Ensure controller/module is powered
- Verify correct port and driver selection
Connection Established but No Response?
- Verify correct protocol configuration (Modbus/serial)
- Confirm correct register/function addressing
- Check device mode is active and not faulted
- Ensure proper polling interval
Intermittent or Unstable Communication?
- Inspect cable shielding and grounding
- Check for electrical noise or interference
- Verify stable power supply
- Confirm proper termination for RS485
Incorrect Data or Values?
- Verify correct register mapping and address
- Check data type (coil, register, analog)
- Confirm scaling and engineering units
- Ensure correct byte/word interpretation
Read Works but Write Fails?
- Confirm register is writable
- Check function code used for write
- Verify correct data format and value range
- Ensure device not in protected mode
Module or Device Not Responding Properly?
- Verify module configuration and addressing
- Restart device and communication interface
- Check communication port selection
- Test with known good cable or device
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