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Option 232 factory configures the WattNode® Modbus meter for an RS-232 compatible communications interface.

This option eliminates the need for a USB/RS-485 adapter when the master host device is already equipped with an RS-232 port and you only need to communicate with one WattNode meter on that port.

RS-232 only supports a single “point-to-point” connection, in contrast to RS-485, which supports “multi-drop” connections where many WattNode meters can communicate with the master through a common bus.

RS-232 is seldom used on modern equipment due to its maximum distance (50 feet vs. 4000 feet for RS-485) and its single slave device limitation. However, RS-232 is commonly available on older PCs and some other devices.

The WattNode meter does not use the RS-232 ‘CTS’ or ‘RTS’ hardware handshake signals since the Modbus protocol automatically handles data flow control through software. The ‘TD’ (transmit), ‘RD’ (receive) and ‘SG’ (signal ground) lines are the only RS-232 signal lines used with Option 232. The WattNode meter supplies its own power for the RS-232 interface and does not “steal” power from the RS-232 signals.

On the WattNode meter, the ‘TD’ (Transmit Data) signal is an output and the ‘RD’ (Receive Data) is an input. So on a PC compatible DB9 COM port connector, the meter A terminal should be connected to pin 2 (the PC’s RD input), the B terminal to pin 3 (the PC’s TD output) and the C terminal to pin 5 (SG). RS-232 serial port connector pinouts for other devices may vary. Ensure the output of the meter connects to the input of other device and vice versa.

WattNode MODBUS Terminal RS-232 Signal Description
A TD Transmit Data
B RD Receive Data
C SG Signal Ground
X Used for other options

This is a special order item. Contact the factory for availability and price.


  • This is a hardware option that cannot be changed in the field.
  • The Modbus RS-232 lines are rated to handle 15kV of ESD (electrostatic discharge).

See Also

Keywords: RS232, EIA232, EIA-232, UART