Communications D - 8
Loopback Test (08H)
The loopback test returns the command message directly as the response message without changing the contents to check the
communications between the master and slave. Set user-defined test code and data values.
The following table shows a message example when performing a loopback test with the slave 1 Drive.
Fig D.8 Function Code 08H Message Example
Write In Several Holding Registers (10H)
Write the specified data to the registers from the specified addresses. The written data must be consecutive, starting from the
specified address in the command message: Higher 8 bits, then lower 8 bits, in storage register address order.
The following table shows an example of a message when a forward run command has been set at a speed command of
60.0 Hz in the slave 1 Drive by the PLC.
Fig D.9 Function Code 10H Message Example
Command Message
Response Message
(During Normal Operation)
Response Message
(During Error)
Slave address
01H
Slave address
01H
Slave address
01H
Function code
08H
Function code
08H
Function code
89H
Test Code
Higher
00H
Test Code
Higher
00H
Error Code
01H
Lower
00H
Lower
00H
CRC-16
Higher
86H
Data
Higher
A5H
Data
Higher
A5H
Lower
50H
Lower
37H
Lower
37H
CRC-16
Higher
DAH
CRC-16
Higher
DAH
Lower
8DH
Lower
8DH
Command Message
Response Message
(During Normal Operation)
Response Message
(During Error)
Slave Address
01H
Slave Address
01H
Slave Address
01H
Function Code
10H
Function Code
10H
Function Code
90H
Start
Address
Higher
00H
Start
Address
Higher
00H
Error code
02H
Lower
01H
Lower
01H
CRC-16
Higher
CDH
Quantity
Higher
00H
Quantity
Higher
00H
Lower
C1H
Lower
02H
Lower
02H
No. of data
04H
CRC-16
Higher
10H
Lead data
Higher
00H
Lower
08H
Lower
01H
Next data
Higher
02H
Lower
58H
* No. of data = 2 x (quantity)
CRC-16
Higher
63H
Lower
39H
IMPORTANT
Set the number of data specified using command messages as quantity of specified messages x 2. Handle
response messages in the same way.
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