Delta ASD-A3-0121, User Manual

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MODBUS Communication ASDA-A3
9-12
Revision December, 2017
9
CRC (RTU mode):
To calculate the CRC value:
Step 1: Load a 16-bit register of FFFFH, which is called the ‟CRC” register.
Step 2: (The low byte of the CRC register) XOR (The first byte of the command), and save the
result in CRC register.
Step 3: Check the least significant bit (LSB) of the CRC register. If the bit is 0, right move one bit;
If the bit is 1, then right move one bit and (CRC register) XOR (A001H). Repeat this step
8 times.
Step 4: Repeat the procedure from step 2 and step 3 until all bytes have been processed. The
content of the CRC register is the CRC value.
After calculating the CRC value, fill in the low word of the CRC value in the command
message, and then the high word. For example, if the result of CRC calculation is 3794H,
put 94H in the low word and put 37H in the high word as shown below:
ARD 01H
CMD 03H
Start Data Address
01H (High)
01H (Low)
Data Number (In words)
00H (High)
02H (Low)
CRC Check Low 94H (Low)
CRC Check High 37H (High)