Enhanced Modbus Functionality for RIO Pocket PLC

Galil recently enhanced the feature set of their RIO-471xx Pocket PLC to include more Modbus functionality. Modbus is one of the open communication protocols in the automation industry and is supported by a majority of automation devices including PLC's, HMI's, sensors and much more. Open communication protocols, such as Modbus, allow different components from different vendors to communicate with each other.

The new RIO enhancements allow it to communicate seamlessly to Think & Do software via Modbus TCP/IP. Think& Do is a software package offered by Entivity that allows a standard computer to act as a PLC for remote IO units. This type of software is often referred to as a "soft PLC". The Think & Do software suite implements numerous communication protocols, including Modbus TCP/IP. The software also provides a user interface that allows the user to control all the equipment in their automation system, including RIO’s, from one program.

Enhancements to the RIO Modbus feature set allow it to work easily with Think & Do software and numerous other Modbus TCP/IP devices. These enhancements, which are available in RIO firmware version 1.0b, include:

1) Supporting Modbus function code 15 as a slave

2) Swapping how function codes 3 and 4 work (MV command)

3) Set data transfers as 16 bit integers as opposed to 32-bit floating point values (MI command)

Function Code 15

In the prior RIO firmware, version 1.0a, function code 15 is only supported as a Modbus master. In the new version 1.0b firmware, Galil has added support for function code 15 as a Modbus slave. This allows other devices to set multiple digital outputs on the RIO at the same time.

MV Command

The RIO will default to answering function code 3 requests with analog input data and function code 4 requests with analog output data. By specifying MV1, the function codes are inverted, and the RIO will respond to function code 3 requests with analog output data and function code 4 requests with analog input data. By having the ability to swap how these requests are handled the RIO becomes flexible enough to communicate with any Modbus enabled device.

MI Command

By default, the RIO will conduct data transactions for function codes 3, 4 and 16 as 32-bit floating point values. By setting MI1, the RIO will use 16-bit integers instead. This functionality allows the controller to conform to the data transaction method of what ever Modbus device it is communicating with.

Example

Consider an automobile plant that has hundreds of different sensors, buttons and general IO across a large area. To coordinate the various devices, the plant manager selected Think & Do software because of its ability to talk to many different types of hardware. Multiple RIO units were selected to monitor the numerous analog and digital IO. With the recent additions to the RIO firmware, the task of having Think & Do communicate with the RIOs is easy; the commands MI1 and MV1 are set on the RIO controllers and they are ready to go. When configured properly, Think & Do software sends Modbus function code 15 requests to the respective RIO in order to query that RIO’s digital outputs. This means that the software can react to changes in the digital IO for all the RIOs in the plant at the same time and with minimal set-up. The RIO Pocket PLC, along with the Think & Do software package provides a cost- effective, easy-to-use method of controlling a distributed IO network.

For more details on the RIO Pocket PLC, please refer to the RIO user manual and command reference at www.galilmc.com/pocketplc or talk to a Galil Applications Engineer at 1-800-377-6329.