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The WattNode Modbus meter has never responded to Modbus messages. The COM LED either blinks red or blinks yellow, regardless of which address we try.

LED Indications

Red Solid

The DIP switches are probably all set to 0 OFF. This is an invalid address and must be changed.

Red Flash

This indicates a baud rate mismatch, parity mismatch, A and B lines swapped, noise, or corrupted RS485 signals.

  • Make sure DIP switch 8 is ON if you are using 19200 baud or OFF for 9600 baud.
  • Make sure the master is set to eight data bits, no parity, and one stop bit (unless you have configured the WattNode meter for even parity).
  • Try swapping the A and B RS-485 lines going into the meter. Generally the WattNode can autodetect if these are swapped, but this can fail in certain cases.
  • Make sure the C (common) line is connected at the WattNode meter and at the Modbus master device.

Yellow Flash

The packets appear to have the correct baud rate and parity, but are not addressed to this WattNode. It is normal to see yellow flashing when other devices on the bus are communicating.

  • Try setting the WattNode DIP switch 1 to the ON position and 2-7 to the OFF position and set the Modbus master to use slave address 1.
  • Try disconnecting all other devices to make sure their messages aren’t causing the yellow flashing.

Red-Yellow-Red-Yellow Flashing

The WattNode was about to respond to a message when it detected traffic on the RS-485 bus. This could be from the Modbus master sending extra characters, another device on the bus responding (generally due to an address conflict), or noise on the bus.

  • Try temporarily disconnecting all other devices from the bus to rule out duplicate addresses.
  • Make sure the Modbus master isn’t sending any extra characters after the end of the packet. Even a brief pulse can cause problems.
  • Make sure the bus isn’t overloaded. If the WattNode cannot see echoes of the bytes it is sending, it assumes their may be a bus conflict.