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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 AlSJ71C24 using the dedicated command
( l T )
with the
dedicated protocols 1 to 4.
The procedure to execute the loopback test is as follows:
Step 1
Connect the computer and AlSJ71C24
Connect the cable between the computer and AlSJ71C24 as
described in Section 4.5.
Step 2
Mode switch settings
Set the mode switch to "1" to "4" to set the testing interface for the
dedicated protocol. (Section 4.3.1 gives detail of thesetting method.)
Step 3
PC CPU start-up
Turn the power to the PC CPU ON or reset the PC CPU. The
AlSJ71C24 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 AlSJ71C24
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 AlSJ71 C24.
Section 8.4 gives the message structure of formats 1 to 4, and
Section 8.15 gives the loopback command (TT).
(2) The AlSJ71C24 transmits the unchanged data back to the
computer.
Step
5
Computer consistency check
(1) Check at the computer if data transmitted from the computer to
the AlSJ71C24 is identical with the data transmitted back from
the AlSJ71C24 to the computer.
Identical data indicates that the communication between the
computer and AlSJ71C24 is normal.
If the data transmitted from the computer to the AlSJ71C24 and
the data transmitted back from the AlSJ7lC24 to the computer
are not identical, the transmission specification settings probab-
ly 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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