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4.
SETTINGS AND PROCEDURES BEFORE OPERATION
MELSEC-A
4.7
Loopback
Test
The loopback test checks the correctness of data communications between
the computer and the AJ71C24 using the dedicated command (TT) with the
dedicated protocols 1 to 4.
The procedure to execute the ioopback test is as follows:
Step 1
Connect the computer and AJ71 C24
Connect the cable between the computer and AJ71C24 as described
in Section 4.5.
Step 2
Mode switch settings
Set the mode switch to "1" to "D" to set the testing interface for the
dedicated protocol. (Section 4.3.1 gives detail of the setting method.)
Step
3
PC CPU start-up
Turn the power to the PC CPU ON or reset the PC CPU. The AJ71 C24
ready signal turns ON (ready for operation), after which the loopback
test can be executed.
(The ready signal turns ON at a few seconds after the AJ71C24 is
turned ON or reset.)
Step 4
Execute the loopback test command
(1) Create a program to be tested and transmit the command and
data to the AJ71 C24.
Section 8.4 gives the message structure of formats 1 to 4, and
Section 8.15 gives the ioopback command (TT).
(2) The AJ71C24 transmits the unchanged data back to the com-
puter.
Step 5
Computer consistency check
(1) Check at the computer if data transmitted from the computer to
the AJ71 C24 is identical with the data transmitted back from the
AJ71C24 to the computer.
Identical data indicates that the communication between the
computer and AJ71C24 is normal.
If the data transmitted from the computer to the AJ71C24 and
the data transmitted back from the AJ71 C24 t o the computer are
not identical, the transmission specification settings probably
do not match or the CD terminal is repeatedly turning ONIOFF.
Use the troubleshooting charts in Sections 11.2.5 and 11.2.6 to
determine and correct the problem. Then repeat the loopback
test.
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