Mitsubishi MELSEC LJ71C24, User Manual

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6 SETTING AND WIRING
6.5 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 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 C24 to an external device
Turn off the power to the station on which the C24 is installed and connect a
communication cable to an external device to perform data communication using the
MC protocol (Refer to Sections 6.2 and 6.3).
(Procedure 2) Switch setting with GX Works2
(1) Set the switch settings with GX Works2 as shown in Section 7.3 and write the
parameters to the CPU module 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.
Item Setting value
Operation setting Independent
Data Bit 7
Parity Bit Exist
Odd/even parity Odd
Stop bit 1
Sum check code None
Online Change Enable
Transmission
Setting
Setting modifications Disable
Communication rate setting 9600bps
Communication protocol setting MC protocol (Format 1)
Station number setting 0
(Procedure 3) Performing a loopback test
(1) Set the CPU module to the STOP status, and turn on or reset the CPU module
(communication is enabled for approx. one second).
(2) Create a program for a loopback test on the external device side and send a
command message such as the following to the C24.
The commands used are as follows:
•
When performing communication test in an A compatible 1C frame:
TT command (For an example, refer to the next page)
•
When performing communication test in a QnA compatible frame:
0619 command
When performing communication tests in a QnA compatible frame, refer to the
following.
MELSEC-Q/L MELSEC Communication Protocol Reference Manual