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4
FUNCTIONS
4.3 RAS Functions
4.3.2 Loopback function
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OVERVIEW
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SYSTEM
CONFIGURATION
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SPECIFICATIONS
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FUNCTIONS
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PREPARATORY
PROCEDURES BEFORE
OPERATION
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LINK DATA SEND/
RECEIVE PROCESSING
AND PROCESSING TIME
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TROUBLESHOOTING
4.3.2 Loopback function
This function disconnects a faulty part such as a disconnected cable or a faulty station
from the network, allowing data link to continue among normally operating stations. (Not
provided for the MELSECNET/B data link system)
Normally, data link is performed using the forward loop.
(1) When an error occurs on the forward loop
When a cable disconnection or a cable connector failure occurs on the forward loop,
data link using the forward loop is not executable.
In such a case, the system automatically switches the line from the forward loop to the
reverse loop to continue data link.
(2) When errors occur on the forward and reverse loops
When cable disconnections or cable connector failures occur on the forward and
reverse loops, data link using these loops is not executable.
Viewing from the master station, loopback occurs at the station just before the fault,
and data link is performed among data-link-executable stations only. (All stations
located between the faulty stations are disconnected.)
Figure 4.11 When an error occurs on the forward loop
Figure 4.12 When errors occur on the forward and reverse loops
Master station
No.5 No.3
No.2
No.1
No.4
Disconnected
Forward loop
Reverse loop
Master station
No.5,
loopback station
No.3
No.2,
loopback station
No.1
No.4
Disconnected
Disconnected
Forward loop
Reverse loop