Hitachi WJ Series

Chapter 11 RS485 Communication
11-1-6
■ (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.
Data name
Description
Coil
Readable/writable binary data (1-bit length)
Holding register
Readable/writable 16-bit length data
 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
16
+X
15
+X
2
+ 1) is used to generate the CRC code.
 The CRC code is 16-bit data generated for a block of arbitrary data length in 8-bit units.
CRC-16
calculation
CRC
*1
=FFFFh
Hi
Low
CRC register (2 bytes)
*1. CRC format
Object data
Swapping high bytes and
low bytes in CRC
*1
Exit
CRC
*1
= CRC
*1
XOR target data
8-bit shift
CRC
*1
= Shift CRC
*1
by 1 bit to the right
Single bit shifted out
CRC
*1
= CRC
*1
XOR A001h
Yes
Object data
Exit
Exit
There is a
remaining bit.
0
1
Shifting by 1byte to the target data