Why do my Read_Var or Write_Var blocks appear to “freeze” and do no recover after I disconnect and then reconnect the ethernet cable from my M580 PLC?
If the cable between the M580 and the server device is disconnected momentarily and the above communication function blocks do not recover, then it is possible the old requests (before disconnection) are being buffered by the server device or gateway.
After the cable is reconnected, the buffer may not clear before the timeout of the communication blocks, preventing them from recovering.
This behaviour can be verified by conducting a Wireshark trace.
To resolve this issue, it is necessary to activate each block after a timeout (eg 10 plc scans) in a cyclic manner, using the Enable pin (see example below).
After the cable is reconnected, the buffer may not clear before the timeout of the communication blocks, preventing them from recovering.
This behaviour can be verified by conducting a Wireshark trace.
To resolve this issue, it is necessary to activate each block after a timeout (eg 10 plc scans) in a cyclic manner, using the Enable pin (see example below).
Released for: Schneider Electric Australia
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