Mitsubishi MELSEC-A Series Reference Manual page 303

10. TROUBLESHOOTING
"A" column: An error will occur to the master station for the third tier if there is an
error in the third tier link parameters set for the corresponding
station.(D9220 to D9223)
When the both inputs (X) and outputs (Y) are not set to a remote I/O
station with link parameters or when I/O assignment of the master
station and installation position of the I/O module of the host station are
wrong, an error will occur.
"0": Normal
"E": Error
"B" column: Displays whether a local station has detected an error at other local
stations.(D9216 to D9219)
"0": Error has not been detected.
"E": Error has been detected.
Only "0" is displayed for a remote I/O station.
"C" column: Displays the forward loop line status of each slave station.(D9232 to
D9239)
"0": Normal
"E": Error
"D" column: Displays the reverse loop line status of each slave station.(D9232 to
D9239)
"0": Normal
"E": Error
POINT
(1) In the MELSECNET data link system, forward/reverse loop errors of the
master station and slave stations are detected at the receive end.
Possible causes for forward/reverse loop errors are as follows:
(a) Broken or loose loop cable connection
(b) Hardware failure at receive end
(c) Hardware failure at send end
In the system configuration shown below, if the forward loop of L3 becomes
faulty, the forward loop cable that connects L2 to L3 might be broken or loose,
the hardware at the forward loop send end of L2 might be faulty, or the
hardware at the forward loop receive end of L3 might be faulty.
If the cable that connects L5 and R6 is broken or loose, a reverse loop error
for L5 will occur.
(2) If the status of a slave station displayed in "L" column is "D", the previous data
in the "S", "A", "B", "C", and "D" columns will remain unchanged.
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