I would like some help about implementing the Modbus RTU communications protocol in an automated system that I am trying to develop. I am confused about how to generally set up my network because I have never used modbus and am generally new at programming PLCs.

I want to monitor the temperature of an oven that is held by a Watlow F4 temperature controller. It requires Modbus RTU communication through an RS-232C interface. I want to constantly read the temperature in the oven and process the data through my PIC microcontroller, which will then communicate back to the F4 controller to adjust the temperature accordingly.

-In this case, will the PIC controller be my client, while my F4 controller is the server? -Is the Modbus RTU protocol simply a way to structure the data transmission, or do I need to download software that uses the modbus implementation? In other words, is the Modbus RTU protocol simply the way you should structure your code to accept and transmit the data packets between the client and server? -Is it possible to simply program the PIC to automate the temperature indefinitely without having a terminal like a PC be the client?

I want to make sure I am understanding the general structure of my project and whether there are any issues with the way I will set up my Modbus network. Please let me know what I can do. Thank you for your time.


1 Answer 1


RS-232 are point to point connection this meant you can only connect the wires to a master and a slave as apposed to RS-485 which can be multydrop.

modbus is a fairly easy to work with it just reading and writing to registers. take a look at this link these guys give you a lot of information.

At the start of your question you mention PLC is that correct or men to be PIC as a lot of PLC have built in modbus and with easy to work with library. PLC also come industrial ready and tested and do not require a PC. A PLC would be a better solution then a PIC if your not wanting to make a PCB and wanting a reliable controller.

Even better remove the Watlow F4 temperature controller and use the PLC with a HMI to do it all. if the wiring is simple. wire the temp sensor to the PLC input and the Heater on/off or/and up/down to the output.

If you still want to use a mico i would recommend using arduino to do this as it easier to get started, the code is simpler to work with and there is lots of examples. this guy id using RS-485 but it will give you an idea if how it done link.


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