Delta C2000 Series User Manual page 407

Check sum
ASCII mode:
LRC (Longitudinal Redundancy Check) is calculated by summing up, module 256, and the values
of the bytes from ADR1 to last data character then calculating the hexadecimal representation of the
2's-complement negation of the sum.
For example,
01H+03H+21H+02H+00H+02H=29H, the 2's-complement negation of 29H is D7H.
RTU mode:
CRC (Cyclical Redundancy Check) is calculated by the following steps:
Step 1:
Load a 16-bit register (called CRC register) with FFFFH.
Step 2:
Exclusive OR the first 8-bit byte of the command message with the low order byte of the 16-bit CRC
register, putting the result in the CRC register.
Step 3:
Examine the LSB of CRC register.
Step 4:
If the LSB of CRC register is 0, shift the CRC register one bit to the right with MSB zero filling, then
repeat step 3. If the LSB of CRC register is 1, shift the CRC register one bit to the right with MSB
zero filling, Exclusive OR the CRC register with the polynomial value A001H, then repeat step 3.
Step 5:
Repeat step 3 and 4 until eight shifts have been performed. When this is done, a complete 8-bit
byte will have been processed.
Step 6:
Repeat step 2 to 5 for the next 8-bit byte of the command message. Continue doing this until all
bytes have been processed. The final contents of the CRC register are the CRC value. When
transmitting the CRC value in the message, the upper and lower bytes of the CRC value must be
swapped, i.e. the lower order byte will be transmitted first.
The following is an example of CRC generation using C language. The function takes two
arguments:
Unsigned char* data
Unsigned char length
The function returns the CRC value as a type of unsigned integer.
Unsigned int crc_chk(unsigned char* data, unsigned char length)
Chapter 12 Description of Parameter Settings C2000 Series
a pointer to the message buffer
the quantity of bytes in the message buffer
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