Modbus TCP in Wattmon

This section introduces you to the way Wattmon handles Modbus TCP connection.

Modbus is an industry standard communication protocol that involves a master/slave configuration.  A master device (the Wattmon in this case) sends a request to read or write registers in a slave device.  Originally this was only possible over a physical wire, usually RS-485 or RS-232.  This is called Modbus RTU.  As networks became more prevalent, a new way of communicating was introduced - Modbus TCP.  This format is very similar to the original RTU format except for a special header and that fact that it works over Ethernet. 

The main advantage of this is of course speed and the fact that it can be installed over a large area network.

Modbus TCP devices have a Modbus device ID just like with Modbus RTU.  Additionally, a device will be reachable on an IP address and port.  The default port for Modbus TCP is 502 but this can usually be set by the device.

Simple Modbus devices such as inverters will have a single ID (usually 1) but some devices such as cluster controllers or Modbus TCP Gateways may have multiple devices services by the same IP address.  We have therefore adopted the term Channel to denote a TCP connection.  Therefore, we have chosen to separate the concept of Channel and Device. 

Configuring Channels

To configure your Modbus TCP Channels, go to Devices and click Options > Edit Communication Settings. 

 The WattmonPRO and MINI have only 1 channel available.  WattmonMEGA has up to 10 channels

Configure the IP address and port for each of the channels you wish to use,  and ensure that the Modbus TCP engine is enabled on the same page.

Configurating Devices

Devices are added using the Manually Add a device option in the Add drop down on the Devices page.  Select the channel you wish to use (Modbus RTU is the default) and save the device. You can always edit it later and shift it to a different channel if necessary.

 You can only add one device with the same ID per channel but you can have multiple devices with the same ID as long as they are on different channels.