You can control the precise order you want SAC to scan your blocks and chains by adjusting the database's scanning order, called the order of solve. Typically, you only need to adjust the order of solve when the value of one block depends on the value of another. For example, suppose you are calculating a value from three Analog Input blocks as the following figure shows.
Sample Calculation Chain
Also assume that by default SAC scans AI1 first, AI2 second, and AI3 third. Because SAC scans AI1 first, it processes the entire chain, computing the value of the Calculation block, before it scans AI2 and AI3. If either of these values change during the current scan cycle, the Calculation does not receive them until AI1 is processed again.
Changing the scanning order addresses this potential problem. By scanning AI1 last, you ensure SAC has updated values for both AI2 and AI3 prior to computing the value of the Calculation block.
You can also phase the blocks so that SAC scans AI1 last. To learn more about phasing, refer to the Phasing section.
