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Modbus RTU

 
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PavelM



Joined: 06 Oct 2021
Posts: 2

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Modbus RTU
PostPosted: Wed Oct 06, 2021 6:44 am     Reply with quote

Hello, i'm trying to communicate with HMI Weintek MT6070iH through Modbus RTU. My device is PIC18F87k90 - slave, HMI - master.
PCH Compiler v. 5.101.



Here is my wiring diagram of max485 which I use.
The code is pretty much copy of ex_modbus_slave.c code.

Code:
#include <main.h>

#define MODBUS_PROTOCOL MODBUS_PROTOCOL_SERIAL
#define MODBUS_BUS SERIAL
#define MODBUS_TYPE MODBUS_TYPE_SLAVE
#define MODBUS_SERIAL_TYPE MODBUS_RTU
#define MODBUS_SERIAL_INT_SOURCE MODBUS_INT_RDA
#define MODBUS_SERIAL_RX_ENABLE PIN_J4
#define MODBUS_SERIAL_ENABLE_PIN PIN_J4
#define MODBUS_SERIAL_BAUD 9600
#define MODBUS_ADDRESS 10

#include "modbus.c"

void main()
{
   int8 coils = 0b00000101;
   int8 inputs = 0b00001001;
   int16 hold_regs[] = {0x8800,0x7700,0x6600,0x5500,0x4400,0x3300,0x2200,0x1100};
   int16 input_regs[] = {0x1100,0x2200,0x3300,0x4400,0x5500,0x6600,0x7700,0x8800};
   int16 event_count = 0;

   setup_adc_ports(NO_ANALOGS);

   modbus_init();

   while(TRUE)
   {
      if(!modbus_kbhit())
      delay_us(50);

      //check address against our address, 0 is broadcast
      if((modbus_rx.address == MODBUS_ADDRESS) || modbus_rx.address == 0)
      {
         switch(modbus_rx.func)
         {
      //check address against our address, 0 is broadcast
      if((modbus_rx.address == MODBUS_ADDRESS) || modbus_rx.address == 0)
      {
         switch(modbus_rx.func)
         {
            case FUNC_READ_COILS:    //read coils
            case FUNC_READ_DISCRETE_INPUT:    //read inputs
               if(modbus_rx.data[0] || modbus_rx.data[2] ||
                  modbus_rx.data[1] >= 8 || modbus_rx.data[3]+modbus_rx.data[1] > 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else
               {
                  int8 data;

                  if(modbus_rx.func == FUNC_READ_COILS)
                     data = coils>>(modbus_rx.data[1]);      //move to the starting coil
                  else
                     data = inputs>>(modbus_rx.data[1]);      //move to the starting input

                  data = data & (0xFF>>(8-modbus_rx.data[3]));  //0 out values after quantity

                  if(modbus_rx.func == FUNC_READ_COILS)
                     modbus_read_coils_rsp(MODBUS_ADDRESS, 0x01, &data);
                  else
                     modbus_read_discrete_input_rsp(MODBUS_ADDRESS, 0x01, &data);

                  event_count++;
               }
               break;
            case FUNC_READ_HOLDING_REGISTERS:
            case FUNC_READ_INPUT_REGISTERS:
               if(modbus_rx.data[0] || modbus_rx.data[2] ||
                  modbus_rx.data[1] >= 8 || modbus_rx.data[3]+modbus_rx.data[1] > 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else
               {
                  if(modbus_rx.func == FUNC_READ_HOLDING_REGISTERS)
                     modbus_read_holding_registers_rsp(MODBUS_ADDRESS,(modbus_rx.data[3]*2),hold_regs+modbus_rx.data[1]);
                  else
                     modbus_read_input_registers_rsp(MODBUS_ADDRESS,(modbus_rx.data[3]*2),input_regs+modbus_rx.data[1]);

                  event_count++;
               }
               break;
            case FUNC_WRITE_SINGLE_COIL:      //write coil
               if(modbus_rx.data[0] || modbus_rx.data[3] || modbus_rx.data[1] > 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else if(modbus_rx.data[2] != 0xFF && modbus_rx.data[2] != 0x00)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_VALUE);
               else
               {
                  if(modbus_rx.data[2] == 0xFF)
                     bit_set(coils,modbus_rx.data[1]);
                  else
                     bit_clear(coils,modbus_rx.data[1]);

                  modbus_write_single_coil_rsp(MODBUS_ADDRESS,modbus_rx.data[1],((int16)(modbus_rx.data[2]))<<8);

                  event_count++;
               }
               break;
            case FUNC_WRITE_SINGLE_REGISTER:
               if(modbus_rx.data[0] || modbus_rx.data[1] >= 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else
               {
                  hold_regs[modbus_rx.data[1]] = make16(modbus_rx.data[2],modbus_rx.data[3]);

                  modbus_write_single_register_rsp(MODBUS_ADDRESS,
                               make16(modbus_rx.data[0],modbus_rx.data[1]),
                               make16(modbus_rx.data[2],modbus_rx.data[3]));
               }
               break;
            case FUNC_WRITE_MULTIPLE_COILS:
               if(modbus_rx.data[0] || modbus_rx.data[2] ||
                  modbus_rx.data[1] >= 8 || modbus_rx.data[3]+modbus_rx.data[1] > 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else
               {
                  int i,j;

                  modbus_rx.data[5] = swap_bits(modbus_rx.data[5]);

                  for(i=modbus_rx.data[1],j=0; i < modbus_rx.data[1]+modbus_rx.data[3]; ++i,++j)
                  {
                     if(bit_test(modbus_rx.data[5],j))
                        bit_set(coils,7-i);
                     else
                        bit_clear(coils,7-i);
                  }

                  modbus_write_multiple_coils_rsp(MODBUS_ADDRESS,
                                 make16(modbus_rx.data[0],modbus_rx.data[1]),
                                 make16(modbus_rx.data[2],modbus_rx.data[3]));

                  event_count++;
               }
               break;
            case FUNC_WRITE_MULTIPLE_REGISTERS:
               if(modbus_rx.data[0] || modbus_rx.data[2] ||
                  modbus_rx.data[1] >= 8 || modbus_rx.data[3]+modbus_rx.data[1] > 8)
                  modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_DATA_ADDRESS);
               else
               {
                  int i,j;

                  for(i=0,j=5; i < modbus_rx.data[4]/2; ++i,j+=2)
                     hold_regs[i] = make16(modbus_rx.data[j],modbus_rx.data[j+1]);

                  modbus_write_multiple_registers_rsp(MODBUS_ADDRESS,
                                 make16(modbus_rx.data[0],modbus_rx.data[1]),
                                 make16(modbus_rx.data[2],modbus_rx.data[3]));

                  event_count++;
               }
               break;
            default:    //We don't support the function, so return exception
               modbus_exception_rsp(MODBUS_ADDRESS,modbus_rx.func,ILLEGAL_FUNCTION);
         }
      }
  }

}     


Not sure about
Quote:
#define MODBUS_BUS SERIAL

Haven't found it in libraries and header files.

HMI options - baud rate 9600, parity - even, 8 data bits, 1 stop bit. This options are the same as default options for modbus, I guess.

My test method is to put 1 variable on screen, which reads value from adresses from 0 to 7.

So the panel shows message "PLC not response" and that's it. Any suggestions where to look at?
PavelM



Joined: 06 Oct 2021
Posts: 2

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PostPosted: Wed Oct 06, 2021 7:43 am     Reply with quote

Ok, never mind, guess I'm dumb.
Tested with bit variable - LED on screen is blinking with some delay, which i manually put in code, so i guess, I'm trying to work with wrong memory area, need to double check Weintek HMI manual for proper addressing.
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