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READ_VAR or WRITE_VAR does not re-establish communications after re-connecting cable.

Goals and Symptoms

READ_VAR or WRITE_VAR does not re-establish communications after re-connecting cable.

Causes and Fixes

The READ_VAR or WRITE_VAR does not re-establish communications after re-connecting the
Ethernet TCP/IP cable.

This will occur if the communications timeout is left at the default value of zero (0). A timeout value of
zero 0) will cause the function block to never timeout. This results in the The READ_VAR and
WRITE_VAR block to never close the TCP/IP connection when the Ethernet cable is disconnected
and re-connected. The PLC will need to be stopped and re-started after the Ethernet TCP/IP cable
is re-connected.

(If you can get online and change the slave ip address of the block, build changes, then  change it back
to the wanted address, build changes again, this will also get it to reestablish communications)

To resolve the issue, define a timeout value in the '%MW+2' management word of the READ_VAR
or WRITE_VAR block.
 

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