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4 Modbus Communications Procedure

E5@C Digital Temperature Controllers Communications Manual (H175)

4-1 Data Format

4-1-1 Command Frame

 CRC-16 Calculation Example

Messages are processed one byte at a time in the work memory (a 16-bit register known as the

CRC register).

(1) The CRC register is initialized to H’FFFF.

(2) An XOR operation is performed on the content of the CRC register and the first byte of the

message, and the result is returned to the CRC register.

(3) The MSB is packed with zeroes and the CRC register is shifted 1 bit to the right.

(4) If the bit shifted from the LSB is 0, step 3 is repeated (next bit-shift processing).

If the bit shifted from the LSB is 1, an XOR is performed on the content of the CRC register

and H’A001, and the result is returned to the CRC register.

(5) Steps 3 and 4 are repeated until 8 bits are shifted.

(6) CRC processing continues to the end of the message, as XOR operations are performed

on the content of the CRC register and the next byte of the message, step 3 is repeated,

and the result is returned to the CRC register.

(7) The result of the CRC calculation (value in the CRC register) is appended to the last byte of

the message.

• Example of Appending the Calculation Result

When the calculated CRC value is H'1234, the CRC value is appended to the command

frame as follows.

CRC-16

Low

H'34

High

H'12

Data

CRC-16 calculation range

2 bytes

Slave

address

Function

code

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