Select and Select before operate

Select and Select before operate

What does the SELEC (Select) status have to do with SBO? (Select Before Operate)

Nothing actually. The SELEC (Select) statusbit is set at the variable and broadcast in the network to all clients, as soon as the command window for this variable is opened on one station. This way evaluating the SELEC statement it can be prevented that two command windows can be open for the same variable in the network.
The select before operate (SBO) sends a telegram for the command variable to the station with the S/E bit in the Qualifier Of Command to 1 (Select) which must be acknowledged by the station before the same telegram is sent with the S/E bit 0 (Execute)

This is a migrated post! Originally posted on 22.08.2007 by user markclemens. Please be aware that information can be outdated.