YASKAWA CIMR-G7U Technical Manual page 307

Error Check
Errors are detected during communications using CRC-16. Perform calculations using the following method.
1. The factory setting for CRC-16 communications is usually 0, but when using the MODBUS system, set the
factory setting to 1 (i.e., set all 16 bits to 1).
2. Calculate CRC-16 using MSB as slave address LSB, and LSB as the MSB of the final data.
3. Also calculate CRC-16 for response messages from the slaves, and compare them to the CRC-16 in the
response messages.
MODBUS Message Example
An example of MODBUS command/response messages is given below.
Reading Storage Register Contents
Read the contents of the storage register only for specified quantities whose addresses are consecutive, starting
from a specified address. The contents of the storage register are separated into higher place 8 bits and lower
place 8 bits, and comprise the data within response messages in address order.
The following table shows message examples when reading status signals, error details, data link status, and
frequency references from the slave 2 Drive.
Command Message
Slave Address
Function Code
Higher
place
Start
Address
Lower
place
Higher
place
Quantity
Lower
place
Higher
place
CRC-16
Lower
place
Response Message
(During Normal Operation)
02H Slave Address
03H Function Code
00H Data quantity
Higher
20H
place
Lead stor-
age register
Lower
00H
place
Higher
04H
place
Next stor-
age register
Lower
45H
place
Higher
F0H
place
Next stor-
age register
Lower
place
Higher
place
Next stor-
age register
Lower
place
Higher
place
CRC-16
Lower
place
Individual Functions
Response Message
(During Error)
02H Slave Address
03H Function Code
08H Error code
Higher
00H
place
CRC-16
Lower
65H
place
00H
00H
00H
00H
01H
F4H
AFH
82H
02H
83H
03H
F1H
31H
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