Modbus is popular data communications protocol used for connecting industrial devices. The specification is open and available at the Modbus website.

Simple IoT can function as both a Modbus client or server and supports both RTU and TCP transports. Modbus client/server is used as follows:

  • client: typically a PLC or Gateway -- the device reading sensors and initiating Modbus transactions. This is the mode to use if you want to read sensor data and then process it or send to an upstream instance.
  • server: typically a sensor, actuator, or other device responding to Modbus requests. Functioning as a server allows SIOT to simulate Modbus devices or to provide data to another client device like a PLC.

Modbus is a prompt response protocol. With Modbus RTU (RS485), you can only have one client (gateway) on the bus and multiple servers (sensors). With Modbus TCP, you can have multiple clients and servers.

Modbus is configured by adding a Modbus node to the root node, and then adding IO nodes to the Modbus node.


Modbus IOs can be configured to support most common IO types and data formats:

modbus io config