Communications D - 6
Error Check
Errors are detected during communication using CRC-16. Perform calculations using the following method:
1. The factory setting for CRC-16 communication is typically zero, but when using the Modbus system, set the factory setting
to one (e.g., 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. Calculate CRC-16 for response messages from the slaves and compare them to the CRC-16 in the response messages.
Modbus Function Code Details
Reading/Holding Register Contents (03H)
Read the contents of the storage register only for specified quantities. The addresses must be consecutive, starting from a
specified address. The data content of the storage register are separated into higher 8 bits and lower 8 bits.
The following table shows message examples when reading status signals, error details, data link status, and frequency
references from the slave 2 Drive.
Fig. D.6 Function Code 03H Message Example
Write In Single Holding Register (06H)
Fig. D.7 Function Code 06H Message Example
Command Message
Response Message
(During Normal Operation)
Response Message
(During Error)
Slave Address 02H Slave Address 02H Slave Address 02H
Function Code 03H Function Code 03H Function Code 83H
Start
Address
Higher 00H Data quantity 08H Error code 03H
Lower 20H
1st storage
register
Higher 00H
CRC-16
Higher F1H
Quantity
Higher 00H Lower 65H Lower 31H
Lower 04H
Next storage
register
Higher 00H
CRC-16
Higher 45H Lower 00H
Lower F0H
Next storage
register
Higher 00H
Lower 00H
Next storage
register
Higher 01H
Lower F4H
CRC-16
Higher AFH
Lower 82H
Command Message
Slave address 01H
Function code 06H
Upper 00H Register
Address
Lower 01H
Upper 00H Setting
Data
Lower 03H
Upper 98H
CRC-16
Lower 0BH
Response Message
(During Normal Operation)
Slave address 01H
Function code 06H
Upper 00H Register
Address
Lower 01H
Upper 00H Setting
Data
Lower 03H
Upper 98H
CRC-16
Lower 0BH
Response Message
(During Error)
Slave address 01H
80H + Function Code 86H
Error code 21H
Upper 82H
CRC-16
Lower 78H
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