Mitsubishi Electric QJ71LP21 Reference Manual page 56

3 SPECIFICATIONS
An RD abnormal detection in the forward loop
An RD abnormal detection in the reverse 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 -1R5-1R6"
R
<Loop containing 1M
R
1M 1: Forward loop normal/reverse loop normal
R
1R4 : Forward loop normal/reverse loop normal
1R5 : Forward loop normal/reverse loop normal
<Loop containing 1R1-1R2-1R3>
1R1 : Forward loop "RD" abnormal/reverse loop normal
1R2 : Forward loop normal/reverse loop normal
1R3 : Forward loop normal/reverse loop "RD" abnormal
Loopback with the reverse loop
Remote master station
Remote I/O station
1-1R4-1R5>
Communication disabled
Remote I/O station
1M
R
Loopback
1R5
Remote I/O station
Loopback with the forward loop
MELSEC-Q
Forward loop
normal
Reverse loop
normal
Forward loop
abnormal
Reverse loop
abnormal
Communication disabled
Communication disabled
Remote I/O station
1R1 1R2
Loopback
Loopback
1R4 1R3
Remote I/O station
Communication disabled
Loopback
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