//Using both a direct function and a library
//for CRC16 calculation used in Modbus

#include "CRC16.h"
#include "CRC.h"

byte str[24] =  {0x01,0x03,0x02,0x00,0x30};
byte str2[24] =  {0x01,0x03,0x00,0x01,0x00,0x01};

CRC16 crc;


void setup()
{
  Serial.begin(115200);
  Serial.println(__FILE__);

  // Serial.println("Verified with - http://zorc.breitbandkatze.de/crc.html \n");

  uint16_t crc = ModRTU_CRC(str,5);
  Serial.println(crc,HEX);
  crc = ModRTU_CRC(str2,6);
  Serial.println(crc,HEX);
}


void loop()
{
}


// Compute the MODBUS RTU CRC
uint16_t ModRTU_CRC(byte* 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)
  uint16_t crc2 = crc >> 8;
    crc2 |= crc << 8;
  return crc2;  
}

// -- END OF FILE --