KROHNE MFC 010 C Converter - Manual (Page 93)

MFC010 Interface Manual 91
unsigned short Calculate_Checksum (unsigned char uc_Telegram_Length, unsigned short *Buffer_Pointer )
{
// Declare Local Variables
unsigned char uc_Byte_Loop;
unsigned char uc_Bit_Loop;
unsigned short us_Temporary_Checksum;
// Initialise the checksum value
unsigned short us_Checksum = 0xFFFF;
// Loop through each byte of the telegram Buffer
for (uc_Byte_Loop = 0; uc_Byte_Loop < uc_ Telegram_Length; uc_Byte_Loop++)
{
// XOR the newly indexed buffer location with the current value of the checksum
us_Checksum ^= (*(Buffer_Pointer + uc_Byte_Loop) & 0x00FF);
// Perform an 8 bit rotation and Polynomial addition on the checksum
for(uc_Bit_Loop = 0; uc_Bit_Loop < 8; uc_Bit_Loop++)
{
// Store the current value of the checksum in a temporary local variable
us_Temporary_Checksum = us_Checksum;
// Right shift the Checksum by one bit
us_Checksum >>= 1;
// Was the first bit of he checksum set?
if (us_Temporary_Checksum & 0x0001)
{
// If so, XOR the Checksum with the Polynomial value
us_Checksum ^= 0xA001;
}
}
}
// Return the calculated checksum result
return us_Checksum;
}