Mitsubishi Electric Melsec QJ71LP21 Reference Manual page 76

3 SPECIFICATIONS
An RD abnormal detection in the forward loop
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(c) Precautions in using the optical loop system
1) When the cable is inserted or removed, the line (forward loop/reverse
loop) may be switched, but the data link will be performed normally.
2) When the loopback is being executed due to a cable disconnection,
both the forward and reverse loops may be recognized as normal
depending on the condition of the cable disconnection.
Whether the forward/reverse loop is normal/abnormal is determined by
the status of "RD" (receive) of the loopback station.
(Example)
In the cases described below, the data link continue by dividing the network into
two loops: "1M 1-1N
P
<Loop containing 1M
1M 1: Forward loop normal/reverse loop normal
P
1N 5: Forward loop normal/reverse loop normal
S
1N 6: Forward loop normal/reverse loop normal
S
<Loop containing 1N
1N 2: Forward loop "RD" abnormal/reverse loop normal
S
1N 3: Forward loop normal/reverse loop normal
S
1N 4: Forward loop normal/reverse loop "RD" abnormal
S
Loopback with the reverse loop
An RD abnormal detection in the reverse loop
5-1N 6" and "1N 2-1N
S S S
1-1N 5-1N 6>
P S S
2-1N 3-1N 4>
S S S
Sub-control station
Control station Normal station
1M 1
P
Loopback
1N 6
S
Normal station Normal station
Loopback with the forward loop
MELSEC-Q
3-1N 4."
S S
Forward loop
normal
Reverse loop
normal
Forward loop
abnormal
Reverse loop
abnormal
Normal station
1N 2
S
Loopback
Loopback
1N 5
S
Normal station
1N 3
S
Loopback
1N 4
S
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