Hitachi WJ Series User Manual page 337

Chapter 11
■ (3) Data
 Send data related to the function code.
 The data transmission format varies depending on the function code.
 Among the data used in Modbus communication, the following data formats are supported.
 Modbus communication of WJ-C1 has restrictions on writing to "2 register length parameter".
For details, refer to "Exception code 27h" in "11.2.9 Exceptional Responses".
■ (4) Error checking
 CRCs (Cyclic Redundancy Check) are used for error checking of Modbus-RTU.
 The generation polynomial of CRC-16(X
 The CRC code is 16-bit data generated for a block of arbitrary data length in 8-bit units.
CRC-16
calculation
*1
CRC
Object data
Swapping high bytes and
low bytes in CRC
Exit
Data name
Coil Readable/writable binary data (1-bit length)
Holding register Readable/writable 16-bit length data
=FFFFh
Yes
Object data
Exit
*1
Description
16 15 2
+X +X + 1) is used to generate the CRC code.
*1. CRC format
Hi
CRC register (2 bytes)
*1 *1
CRC = CRC XOR target data
8-bit shift
CRC *1 = Shift CRC *1 by 1 bit to the right
0
Single bit shifted out
*1 *1
CRC = CRC
Shifting by 1byte to the target data
11-1-6
RS485 Communication
Low
Exit
There is a
remaining bit.
1
XOR A001h