Modbus Slave project for PIC18F

This project contains the code to get ANY PIC18F series Microcontroller with a working USART to act as a Modbus Slave device.

The project is ready to go for either the PIC18F8722 or the PIC18F4520 but with some simple changes can work with any other device.

IF USING 18F4520 or 18F8722

To get started make the relevant changes to "System.h" All you need to do is define your processor, frequency, baudrate etc in here and you are ready to go.

From here you can start coding away in "main.c" and start adding your own functions to "user.c".. all you need to do is equate a holdingReg or a coil to something.

For example

void main(void)
{
  OpnUSART();
  ConfigInterrupts();

  while(1){
    if(modbusMessage){
      decodeIt();}

      //Start code here...

      TRISD,TRISC = 0;
      LATD = holdingReg[0];
      LATCbits.LATC1 = coils[0];
    }
}

This code would output whatever is in holdingReg[0] to LATD and whatever is in coils[0] to LATC1.. it is that easy..

Obviously you can take it further than this and start making cool functions but that is up to you.. all of the communication code is taken care for you.

IF USING ANOTHER PROCESSOR

There are some things you are going to need to change.. as you can see in system.h at the bottom there are some #ifdef's defined for the 2 choices of processor.

You will need to make your own ifdef for your processor.. containing the relevant configurations and options.

There are 2 more places that the ifdefs will be needed to be changed and that is in all of the functions inside "system.c" and in "configurationbits.c"

If you look inside the ifdefs in these 2 files it should be clear what they do and what you will need to change to get it working on your processor..

So for example if I wanted to get this going on an PIC18F4550 I would first go to system.h and define it at the top as p18f4550..

Then I would go to the bottom of system.h and make an ifdef use case for the p18f4550, leaving the other 2 ifdefs intact..

I would then go into system.c and add my own ifdef to all the functions and finally create an ifdef in the configuration bits file.. that is all.

Thanks and enjoy :)