Why does my READ_VAR lock up on a M580 HSBY switchover?
Issue
Communication function lockup on HSBY
Product Line
Modicon M580
Environment
EcoStruxure Control Expert
Unity Pro
Resolution
If your READ_VAR is not communicating after the M580 goes through a switchover you may not be following the proper procedure for the HSBY system. Follow procedure below.
Asynchronous Communication Procedures
Communication function lockup on HSBY
Product Line
Modicon M580
Environment
EcoStruxure Control Expert
Unity Pro
Resolution
If your READ_VAR is not communicating after the M580 goes through a switchover you may not be following the proper procedure for the HSBY system. Follow procedure below.
Asynchronous Communication Procedures
During a Switchover event, asynchronous communication procedures: READ_VAR, WRITE_VAR, DATA_EXCH, INPUT_CHAR, INPUT_BYTE, PRINT_CHAR, do not automatically resume operation on the new Primary PLC without special care.
The following procedure should be used to allow asynchronous communication EFs to automatically resume operation after a Switchover:
- Program your application so that all EFs management parameters are not exchanged with Standby PLC. To do this, de-select the Exchange on STBY attribute for the management parameter.
- Initialize the Length parameter each time the function is called.
- Set the Timeout parameter accordingly to your application:
If the communication function is send through the CPU, the typical timeout value is 500 ms.
If the communication function is send through a NOC module, the typical timeout value is 2 s.
NOTE: If for some reason you are unable to follow this procedure, and a Switchover renders your communication function inoperative, write your application program so that it sets the function activity bit to 0 before restarting the function in the new Primary CPU.
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