Issue
READ_VAR or WRITE_VAR does not recover communication after disconnect and reconnect the cable

Root Cause
Default value of Reset Word (Time out value) from READ/WRITE_VAR is Zero. By running this default value of Reset Word will cause the function block to never timeout. Therefore READ/WRITE_VAR will never close the TCP/IP connection when the Ethernet cable is disconnected and reconnected. By doing Stop and Run on PLC can reestablish the communication but is not applicable in most of the actual working situation.

Resolution
Change the Reset Word to an Non-Zero value. Since this value actual means Time out, and is set to times 100ms, so if it is set as 1, it means 100ms, if it is set as 10, it means 10x100ms = 1000ms = 1s. This Reset Word is located in the third variable in GEST array.

For example, if you map your GEST to %MW200:4, then GEST[2] is the third variable in the array, see below pic for more information.