CO2Modbus.c

/*

 * CO2Modbus.c

 *

 * Created: 19.03.2015 17:19:59

 *  Author: Johannes1

 */ 

#include <avr/io.h>

#include "uart0.h"

#include "uart1.h"

#include "util/delay.h"

uint16_t ModRTU_CRC(uint8_t buf[], int len);

int main(void)

{  

  uint8_t buffer[8],crc_low,crc_high,i,c,recchar;

  uint8_t receive_buffer[14];

  uint16_t crc;

  uart0_init(9600,1,1);

  uart1_init_x(9600,1,1,8,0,0,0,2);

  //Baudrate=9600; send..enabled; receive..enabled;8 Databits; send and receive with interrupt disabled

  //2 Stopbits

  //PB7 --> Send /Receive

  DDRB|=(1<<DDB7);

  PORTB|=(1<<PB7);

  //HIGH....Transmit

  //LOW.....Receive

  //Command to read Inputregister

  buffer[0]=0x01;

  buffer[1]=0x04;

  buffer[2]=0x00;

  buffer[3]=0x0C;

  buffer[4]=0x00;

  buffer[5]=0x01;

  buffer[6]=0x00;

  buffer[7]=0x00;

  //Generate CRC

  crc=ModRTU_CRC(buffer,6);

  crc_high=crc>>8;

  crc_low=crc&0xFF;

  //Transmit crc to TeraTerm --> check

    uart0_putCharAsHex(crc_low);

  uart0_putCharAsHex(crc_high);

  //write crc to command

  buffer[6]= crc_low;

  buffer[7]= crc_high;

  //send command via Rs485

  PORTB|=(1<<PB7);

  for(i=0;i<8;i++)

  {

    uart1_putc(buffer[i]);

  }

  while ( (UCSR1A & (1<<TXC1)) == 0);

  //switch to receive Mode

  PORTB&=~(1<<PB7);

  //read response from the RS485 interface

  for(i=0;i<7;i++)

  {

    receive_buffer[i]=uart1_getc();  

  }

  //transmit response to TeraTerm

  for(i=0;i<7;i++)

  {

    uart0_putCharAsHex(receive_buffer[i]);

    uart0_newline();

  }

    while(1)

    {

    }

}

// Compute the MODBUS RTU CRC

uint16_t ModRTU_CRC(uint8_t buf[], int len)

{

  uint16_t crc = 0xFFFF;

  for (int pos = 0; pos < len; pos++) {

    crc ^= (uint16_t)buf[pos];          // XOR byte into least sig. byte of crc

    for (int i = 8; i != 0; i--) {    // Loop over each bit

    if ((crc & 0x0001) != 0) {      // If the LSB is set

    crc >>= 1;                    // Shift right and XOR 0xA001

    crc ^= 0xA001;

  }

  else                            // Else LSB is not set

  crc >>= 1;                    // Just shift right

}

  }

  // Note, this number has low and high bytes swapped, so use it accordingly (or swap bytes)

  return crc;  

}