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MELSEC-Q

4 SETTING AND PROCEDURE BEFORE OPERATION

4.7.1 Self-loopback test

This test checks the internal circuits including the send/receive circuits of the network
module together with the connected cable.

POINT

Always connect a cable or terminating resistors when performing the self-loopback
test.
In addition, do not connect or disconnect the cable or terminating resistors during
the test. (The test completes with an error.)

(1) For the QJ71LP21/QJ72LP25 network module (for the optical loop system),

connect the IN connector and OUT connector with an optical fiber cable.
For the QJ71BR11/QJ72BR15 network module (for the coaxial bus system),
connect terminating resistors to both connectors of the F-type connectors.

For QJ71LP21/QJ72LP25

(optical loop system)

For QJ71BR11/QJ72BR15

(coaxial bus system)

OUT

Connect IN
and OUT

Connect terminating
resistors

MODE

(2) Set the mode setting switch of the network module to "1". Set it to "5" when

using the QJ71LP21/QJ72LP25 at 25Mbps.

RUN

MNG

T.PASS

D.LINK

ERR.

L ERR.

(3) Power on the target station.

The self-loopback test starts and the T.PASS LED flashes.

(4) The test is completed normally when the T.PASS LED flashes 20 or more times

(approx. 10 seconds) and the ERR. LED does not flash. When the test
completes with an error, the ERR. LED flashes.

If an error occurs, perform the following.
• For the QJ71LP21/QJ72LP25 (for the optical loop system), replace the cable

and perform the test again.

• For the QJ71BR11/QJ72BR15 (for the coaxial bus system), replace the

terminating resistors and perform the test again.

When the test completes with an error again, the possible cause is a hardware
failure of the network module. Please consult your local Mitsubishi
representative.