Serial Bus commands have some unique properties when in Pre and post measures.
1.) They will always be emitted, even if the device is already in the same state
This is self explanatory, and is one of the most valuable features of the pre and post measures. It allows the programmer to force the serial write
2.) There will be an emit for every button, even if they are in the same register (unless in a combined group)
This is subtle but important to understand
For instance this panel has three buttons from register06.
This forces three separate writes for register 6. In addition, each write will have the default setting for all the other fields.
Meaning when the first write goes out with the 06_M_Count register at 10, the B count and A count will be at their default settings! (not the ones in the panel!)
In most cases this is not the desired action.
The correct solution is to use the combined group. In this case the three buttons from register06 are put in a combined group before it is put into the premeasure group.
This combined the three field buttons into a single "emit".
This example should give additional insight into how the pre and post measure concept is dealt with in the system compiler.