As blocks change from Automatic and Manual modes, they enter a pending state. This state indicates that SAC has acknowledged the mode switch and will change it on the next scan.
Blocks placed into Manual mode enter PMAN mode. The block remains in this state until SAC scans the block again. While in PMAN mode, SAC continues to scan the block according to its scan time and phase. Manual entries from an operator or a Program block force SAC to scan the block immediately and put it into Manual mode. Scans after a manual entry depend on the block's scan time.
Example: Blocks in PMAN Mode
For blocks with short scan times, the next scan time occurs relative to the manual entry. For example, suppose SAC scans the block AI1 at 1:15:30. This block has a 30-second scan time and a 5-second phase. If an operator puts AI1 into Manual mode and enters a value at 1:15:45, SAC scans the block immediately and resets AI1's next scan to 1:16:15 and every 30 seconds thereafter. If the operator subsequently enters another value at 1:15:50, SAC scans AI1 again and reset AI1's next scan to 1:16:20 and every 30 seconds thereafter.
For blocks with scan times of a minute or longer, SAC synchronizes the next scan to the system clock. For example, assume AI2 has a one hour scan time and a 30-minute phase. If an operator placed the block into Manual mode and enters a value at 15 minutes past the hour, SAC scans AI2 immediately and on the half hour.
