Both of these documents can be found on the Watlow web siteįor example, if you wanted to read analog input 1 on the Watlow MLS300 controller, you would first have to make sure you are using the correct baud rate and slave address for the Watlow controller. When using the Watlow MLS300, most of this information is located in either the MLS3XX Communications Specification or user manual. Generally, to figure this out, you will need to use the documentation for your Modbus device to figure this out. The most challenging part of communicating with a Modbus device is figuring out what address to use and figuring out what to use for some of the other parameters. These 2 inputs to the Query VI are the inputs that tell LabVIEW which registers we are accessing and whether we are writing or reading values.ĭetermining parameters to use in this example for the Watlow MLS300. The main parameters that will need to be changed are the Function Code and Starting Address. This example can be modified very easily to write any outputs or read any inputs that the Modbus device makes available. In this example, you will see that communicating with a Modbus device will involve initializing the port we are using, then using the query command, and finally closing the Port. The Modbus library for LabVIEW is a set of VIs that take Modbus specific inputs and converts those to the appropriate VISA commands. Since Modbus is a serial communications protocol, the VISA driver can be used to send data over the serial port to communicate with a Modbus device.
National Instruments provides a Modbus Library for LabVIEW that is designed to facilitate communication to a device that can use the Modbus protocol. Introduction to the Modbus Library for LabVIEW. The Slave device we are communicating with as an example is the Watlow MLS300 Controller that is connected via serial port. This example shows how to use the Modbus library for LabVIEW to read analog inputs from a Modbus slave device.
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