Hitachi SJ700-2 instruction manual CRC*1

Chapter 4 Explanation of Functions

(iv)Error check code

The Modbus-RTU protocol uses the cyclic redundancy check (CRC) as the error check method.

The CRC code is the 16-bit data generated for a data block that has an arbitrary data length (in units of 8 bits).

A generative polynomial for CRC-16 (X16 + X15 + X2 + 1) is used to generate the CRC code.

Example of CRC-16 calculation

CRC-16 operation

CRC*1 = FFFFh

CRC*1

Hi Lo

CRC register (2 bytes)

Is the target	Yes	Set the XOR of CRC*1 data and
data found?		target data in CRC*1
No
		Does any	No
		bit remain after 8-bit
		shifting?

Replace the Hi and Lo bytes
of CRC*1 with each other	Yes
Shift CRC*1 to the left by 1 bit
No	Is the
	bit put out of
End	CRC*1 "1"?
	Yes
Set the XOR of CRC*1 data
	and A001h in CRC*1

The target data is shifted by 1 byte.

(v)Header and trailer (silent interval)

The header and trailer set the total time the inverter should wait before sending a response after having received a query from the master system.

Be sure to specify the time corresponding to the transmission of 3.5 characters (24 bits) as the waiting time. If a shorter waiting time (corresponding to the transmission of fewer than 3.5 characters) is specified, the inverter will not respond.

The actual waiting time is the sum of the silent interval (corresponding to the transmission of 3.5 characters) and the communication wait time (C078).

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