You can also overphase your blocks. An overphased block is one that has a larger phase than scan time. For example, assume you have the chain shown in the Exception-Based Chain Processing figure. In this chain, AI2 and AI3 have 5-second scan times. AI1 is overphased with a 5-second scan time and a 10-second phase. This delays AI1 by 10 seconds and ensures that SAC scans AI2 and AI3 before AI1. This means that the Calculation block receives the most recent values on which to perform its functions.
Overphasing and Long Scan Times
SAC only lets you overphase blocks with second or subsecond scan times. For blocks with a scan time of a minute or more, you can create an initial offset from the time that SAC would normally scan the block. For example, assume you want to scan a block every 6 hours with an offset of 2 hours and 10 minutes. You can configure the offset by entering the following phase in the Phase field:
2:10
Because the scan time is linked to the system clock, SAC always scans the block at 2:10, 8:10, 14:10, and 20:10 regardless of when it was placed on scan. Also remember, SAC scans blocks with scan times of one minute or longer immediately when iFIX starts or when the database is reloaded. To forego this initial scan, start SAC with the S command line parameter. Refer to the section Controlling SAC Startup in the Setting up the Environment manual for more information on specifying SAC command line parameters.
