YASKAWA G7 Series 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 02H
Function Code 03H
Higher
00H
place
Start
Address
Lower
20H
place
Higher
00H
place
Quantity
Lower
04H
place
Higher
45H
place
CRC-16
Lower
F0H
place
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Response Message
(During Normal Operation)
Slave Address 02H
Function Code 03H
Data quantity 08H
Higher
00H
place
Lead stor-
age register
Lower
65H
place
Higher
00H
place
Next stor-
age register
Lower
00H
place
Higher
00H
place
Next stor-
age register
Lower
00H
place
Higher
01H
place
Next stor-
age register
Lower
F4H
place
Higher
AFH
place
CRC-16
Lower
82H
place
Individual Functions
Response Message
(During Error)
Slave Address 02H
Function Code 83H
Error code 03H
Higher
F1H
place
CRC-16
Lower
31H
place
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