Symptoms

A WattNode Modbus meter ordered with option EP and/or option 38K fails to communicate at even parity and/or 38,400 baud. Instead, it reverts to no parity and the baud rate specified by DIP position 8 (9,600 or 19,200 baud).

Affected Products

Modbus WattNode meters ordered with option EP (even parity) and/or option 38K (38,400 baud) that were manufactured or recalibrated between June 25, 2011 and Oct 10, 2013. If you have a WattNode that is still communicating, you can tell if this issue affects it or not by reading the OptBaudRate and OptParityMode registers 1729 and 1730, respectively. If the OptBaudRate register reads back a value of 6 and the OptParityMode register reads 1, then the WattNode is working properly and immune from this issue.

Synopsis

Communications options should have been programmed into the meter two ways:

  1. The options are stored as the factory options, so that a restore to factory communication configuration will work correctly.
  2. The options are assigned as the currently active communication settings.

Step one was missed in production, so any affected meters would leave the factory with the correct configured settings, but the meters were vulnerable to losing these settings if the meter was powered up for 10 seconds with all DIP switches in the off (down) position (this normally restores the factory communication configuration).

Prevention

For the affected meters, do not allow all eight DIP switches to be in the off (down) position when the meter has power applied. Before powering up the meter, assign the Modbus address with DIP switches 1 to 7. You can change the address again after the meter is powered on, provided that all eight DIP switches are never off (down) for more than 10 seconds (e.g. by leaving DIP switch 8 always on (up)).

Workarounds

By default, WattNode Modbus meters are shipped with all DIP switches off (down). As a result, if the meter is powered up for 10 seconds or longer without changing the DIP switches, and affected meter behaves as if it had not been ordered with the EP and/or 38K options. That is, it uses 8N1 (8 data bits, no parity, 1 stop bit) and 9,600 or 19,200 baud per the DIP switch 8 setting. If your Modbus network can accommodate either of those baud rates at 8N1, simply select which baud rate to use with DIP switch 8. However, no DIP switch setting will configure the communications to the factory configured setting.

If you must use 38K baud and/or even parity, you can reassign the meter’s communications settings if you have access to Modbus master software that can write to arbitrary Modbus registers. You can do this by using the Modbus master software to write to the meter’s Communication registers as described in the user manual. The basic procedure is:

  1. Use your Modbus master software to establish communications with the WattNode using 8 data bits, no parity and 1 stop bit at either 9,600 or 19,200 baud (when DIP switch 8 is off (down) or on (up), respectively).
  2. If you want 38,400 baud, write an integer value of 6 to the BaudRate register at address 1653.
  3. If you want even parity, write an integer value of 1 to the ParityMode register at address 1654.
  4. Write an integer value of 1234 to the ApplyCommConfig register 1651 to make the preceding changes take effect. These new settings are saved to non-volatile memory and will be remembered through power cycling.
  5. You can now communicate with the WattNode at the new serial line settings (e.g. 38K, E81).

If none of these workarounds are possible, you may return the meter and CCS will correctly program the options.

Corrective Action Taken

The CCS production software has been updated (as of October 24, 2013) to perform the necessary step to save the factory communication options. In addition, it also verifies that the settings have been properly saved. Testing was performed to verify the update.

Any WattNode Modbus meter shipped after 10/24/13 with Opt 38K, EP will always operate at 38,400 baud, even parity, regardless of how the DIP switches are set before, during, or after power up. The only way to change the baud rate and parity for meters with factory preconfigured communications settings will be to write to multiple communication configuration registers as described above and in the manual.