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MELSEC-Q
4 SETTINGS AND PROCEDURES PRIOR TO OPERATION
4.8 Loopback Test
A loopback test performs a communication test using the loopback test function of the
MC protocol, in order to check the connection between the Q series C24 and an
external device, the communication function of each device, and the operation of the
communication program of the external device.
(Procedure 1) Connecting the Q series C24 to an external device
Turn off the power to the station on which the Q series C24 is installed and connect a
communication cable to an external device to perform data communication using the
MC protocol (see Section 4.4).
(Procedure 2) Switch setting with GX Developer
(1) Set the switch settings with GX Developer as shown in Section 4.5 and write the
parameters to the PLC CPU in order to perform data communication using the MC
protocol.
(2) The following shows an example of the settings when performing a loopback test
on the interface on the CH1 side.
• Switch 1: 0544
H
Transmission Operation setting : Independent operation
setting Data bit : 7 bit
Parity bit : Yes (odd)
Stop bit : 1 bit
Sum check code : No
Write during RUN : Allowed
Setting modification : Prohibited
Communication rate setting : 9600 bps
• Switch 2: 0001
H
Communication protocol setting : MC protocol (format 1)
• Switch 3: 0000
H
• Switch 4: 0000
H
• Switch 5: 0000
H
Station number setting : 0 station
(Procedure 3) Performing a loopback test
(1) Set the PLC CPU to STOP status, and turn the power on or reset the CPU
(communication is enabled in about one second).
(2) Create a program for a loopback test on the external device side and send a
command message like the one in the example below to the Q series C24.
The commands used are as follows:
• When performing communication test in an A compatible 1C frame: TT
command (for an example, see the following page)
• When performing communication test in a QnA compatible frame: 0619 command
See the Reference Manual when performing communication tests in a QnA
compatible frame.
(Procedure 4) Checking loopback test result
(1) The Q series C24 sends a response message to the external device when it
receives a loopback test command message.
The Q series C24 sends the external device the received data as is.
(2) Check on the external device whether the data received from the Q series C24
matches the data sent from the external device.