Delta ASDA-A3 Series User Manual page 617

MODBUS Communication
CRC (RTU mode):
To calculate the CRC value:
Step 1: load a 16-bit register with the content of FFFFH, which is called the ‟CRC" register.
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Step 2: (The low byte of the CRC register) XOR (The first byte of the command), and save the
result in the CRC register.
Step 3: check the least significant bit (LSB) of the CRC register. If the bit is 0, shift the register
one bit to the right. If the bit is 1, shift the register one bit to the right and execute (CRC
register) XOR (A001H). Repeat this step 8 times.
Step 4: repeat steps 2 and 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 in the following table.
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ARD
CMD
Start Data Address
Data Number (in words)
CRC Check Low
CRC Check High
01H
03H
01H (High)
01H (Low)
00H (High)
02H (Low)
94H (Low)
37H (High)
ASDA-A3