CREATING A REDUNDANT STRATEGY
SNAP PAC Redundancy Option User’s Guide
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variable is synchronized immediately after it is changed, and this can cause your system to slow
down.
To create a persistent/redundant variable, see
“Configuring Redundant Variables” on page
Persistent/Redundant Variables
Most variables can be persistent/redundant. However, pointer variables, pointer tables, and timers
can be redundant but not persistent. Normally, variables are set to an initial value (which you specify
during configuration) either whenever the strategy is run or whenever it is downloaded.
Persistent/redundant variables, however, are initialized only when the strategy is first downloaded.
Persistent variables are initialized with zero until set for the first time, after which the value does not
change unless the strategy or other client changes it. The variable’s value is saved in the controller’s
memory; it does not change when the strategy is run, stopped, or started, and it does not change if
the strategy is changed and downloaded again.
A persistent/redundant variable’s value remains the same until one of the following events occurs:
•
The value is changed with PAC Control Debugger or other client.
•
A strategy with a different name is downloaded.
•
The RAM memory on the controller is cleared.
•
New firmware is downloaded to the controller.
•
The persistent/redundant object is changed as follows:
–
A persistent/redundant table's length (integer, 64-bit integer, float, and string) is modified.
–
A persistent/redundant string variable's length is modified.
–
A persistent/redundant string table element's string length is modified.
–
A persistent/redundant variable's type is changed. For example, a persistent/redundant
float variable is deleted and a new persistent/redundant integer variable is created with the
same name.
•
The strategy writes a new value to the variable.
Configuring Redundant Variables
To add a redundant variable:
NOTE: These are basic instructions only. For more information on configuring variables, see Chapter 9:
Using Variables and Commands in form 1700, the PAC Control User’s Guide.
1.
Make sure that redundancy is enabled for the strategy. See
2.
With the strategy or subroutine open in Configure mode, choose Configure
Variables.
