Modbus RTU function 1 code

Dear all,
I am trying to integrate arduino with modbus RTU protocol. Using previous library i could able to use Holding register i.e function 3 with system. Now i would like to implement using function code 1. Is there any c example code used for reading coil function.

Below function i used to get function 3 & its working fine. Is there any changes to be made to work on function 0X01

nsigned int crc_fn(unsigned char *dpacket,unsigned int len) // CRC Function(Error calcualtion)
{
 unsigned int crc = 0xffff,poly = 0xa001;
 unsigned int i=0; 
   
 for(i=0;i<len;i++)
 {
    crc^= dpacket[i];
    for(j=0;j<8;j++)
    {
     if(crc & 0x01)
     {
      crc >>= 1;
      crc ^= poly;
     }
     else
    crc >>= 1;
    }
 }
 return (crc); 
}

function 03: data input given in Hex 010300000031841E

If i change function code 1 & send input in format 010100000031fdde it will result Invalid Modbus response.