Modbus-RTU-Preset-Multiple-Registers-STM32-As-Slave

A request to pre-set two registers starting at 40001 to 0000H, 00001H, …., and 0009H, in slave device 1. The first register is the LED1 state, the second register is the LED2 state.

Request frame of Master

01 10 00 00 00 02 04 00 00 00 01 32 6F

Field Name	Value (Hex)
Slave Address	01
Function	10
Starting Address Hi	00
Starting Address Lo	00
Number of registers Hi	00
Number of registers Lo	02
Byte count	04
Data Hi	00
Data Lo	00
Data Hi	00
Data Lo	01
CRC Hi	32
CRC Lo	6F

Response frame of Slave

01 10 00 00 00 02 41 C8

Field Name	Value (Hex)
Slave Address	01
Function	10
Starting Address Hi	00
Starting Address Lo	00
Number of registers Hi	00
Number of registers Lo	02
CRC Hi	41
CRC Lo	C8

Library

modbusSlave.c modbusSlave.h modbus_crc.c modbus_crc.h

How to use this Library:

• Include "modbusSlave.h" and create global variables

#include "modbusSlave.h"

uint8_t RxData[256];
uint8_t TxData[256];
uint16_t Holding_Registers_Data[50];

• Write interrupt function

  void HAL_UARTEx_RxEventCallback(UART_HandleTypeDef *huart, uint16_t Size)
  {
    if(huart->Instance == huart2.Instance) // check interrupt of serial port 2
    {
      uint16_t size = sizeof(RxData) / sizeof(RxData[0]);
      uint16_t crc = crc16(RxData, size);
      uint8_t crcLo = crc&0xFF;   // CRC LOW
      uint8_t crcHi = (crc>>8)&0xFF;  // CRC HIGH
      if((RxData[size-1] == crcLo) && (RxData[size-2] == crcHi)) // CRC check
      {
        if (RxData[0] == SLAVE_ID)
        {
          switch (RxData[1])
          {
            case 0x03:
            readHoldingRegs();
  						
            break;
            case 0x04:
            readInputRegs();
  						
            break;
            case 0x01:
            readCoils();
  						
            break;
            case 0x02:
            readInputs();
  						
            break;
            case 0x06:
            writeSingleReg();
  						
            break;
            case 0x10:
            writeHoldingRegs();
  						
            if(Holding_Registers_Data[0]== 1) HAL_GPIO_WritePin(GPIOB, GPIO_PIN_6, 1);
            else if(Holding_Registers_Data[0] == 0) HAL_GPIO_WritePin(GPIOB, GPIO_PIN_6, 0);
  						
            if(Holding_Registers_Data[1] == 1) HAL_GPIO_WritePin(GPIOB, GPIO_PIN_7, 1);
            else if(Holding_Registers_Data[1] == 0) HAL_GPIO_WritePin(GPIOB, GPIO_PIN_7, 0);
  						
            break;
            default:
          	modbusException(ILLEGAL_FUNCTION);
  						
            break;
            }
          }
        }
      else modbusException(ILLEGAL_FUNCTION);
      HAL_UARTEx_ReceiveToIdle_IT(&huart2, RxData, 256);
    }
  }		
  

Demo

Source code