From FieldServer Technologies: [1] http://www.protocessor.com/products/Free_Modbus_RTU_Source_Code.html

• Are you designing an industrial or building automation controller that requires Modbus RTU?
• Do your customers ask for Modbus RTU protocol support?
• Did you know that Modbus RTU is the most popular Industrial Automation protocol in the world?
• Did you know that implementing Modbus RTU on your embedded systems will provide greatest connectivity?

If the answer to any of the above is yes, then this Modbus RTU source code is a good place to start. Obtain the source code by clicking on the link to the right. This code is written for a PIC18f2431 chip, but it can easily be adapted for other CPUs. The steps required to have a functioning Modbus RTU server device are:

Compile our Free Modbus RTU Source Code using the Microchip C18 compiler

Using the [2] Microchip ICD2 debugger module, download the resulting binary image to a [3] PIC18F2431 on the Microchip [4] PICDEM2 Plus evaluation board

Fire up a working Modbus RTU server (slave).

Use our Modbus Simulator to test the communications with your controller.