Block Modes

Blocks can receive data from the following sources:

Other blocks.
An I/O driver or OPC server.
The keyboard (using Data links).
Recipes.
Easy Database Access programs.
Visual Basic for Applications (VBA) scripts.

You can control from where a block receives data by setting its mode, as the following figure shows:

Placing a block in Manual mode does not place it off scan; SAC still processes the block using its last value. manual mode only prevents a block from receiving data from an I/O driver, an OPC server, or the upstream block. SAC also scans exception-based blocks when they change mode (from Automatic to Manual mode or vice versa). While in Manual mode, SAC accepts any input within the EGU range and immediately scans the block. No deadband checking is made on these values.

You can toggle a block's mode from an operator display by adding an object to the display and then using the Toggle Tag Auto/Manual Expert from the Task Wizard. To display a block's mode from an operator display, add a Data link that references the block's A_AUTO field. If you have enabled in-place data entry when configuring the data link, you can then modify that block's mode from the operator display by clicking on the Data link and entering AUTO or MANL. You can also modify a block's mode from the Database Manager by entering AUTO or MANL in the Curr Mode column for the selected block.

NOTE: Blocks perform alarming in both Automatic and Manual modes.

The exact function of certain blocks depends on their mode, as the following table describes

97%;">

Blocks in Automatic and Manual Modes
The block...	In automatic mode...	And in manual mode...
Analog Input	Reads and writes data every scan cycle.	Receives data from operators entering values, scripts, Program blocks, recipes, or Easy Database Access (EDA) programs, but does not output values.
Device Control	Executes all statements without interruption.	Suspends execution until the block is placed in Automatic mode.
Digital Input	Reads and writes data every scan cycle.	Receives data from operators entering values, scripts, Program blocks, recipes, or EDA programs, but does not output values.
PID	Performs PID adjustments. Set points can be changed through a Data link in this mode.	Suspends automatic PID outputs. This allows you to change the output from the block. Block values, such as the set point and tuning parameters, can be changed from the keyboard.
Program	Executes all statements without interruption.	Suspends execution of its statements until the block is placed in Automatic mode. When the block is switched back to Automatic mode, it continues from where it stopped.
Statistical Control	Feeds information back into your process when the Statistical Data block generates an alarm.	Suspends feedback.
Statistical Data	Performs online statistical process control on incoming data from other blocks.	Suspends online data observations. Used for off-line statistical process control.

See Also