Mitsubishi MELSEC-A Series Reference Manual page 97

5. SPECIFICATIONS
(3) Data link when the forward loop is faulty
If data link using the forward loop is disabled due to a broken cable or a problem with
a forward loop cable connector, the loop is automatically switched from "forward" to
"reverse" to maintain the data link.
In the reverse loop, link data is sent in the following order:
master station station No. n station No. (n-1), ....
Data link operation when a forward loop cable is broken or disconnected is illustrated
in Fig 5.5.
Fig 5.5 Reverse loop data link (When one master station and eight slave stations are used)
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