Publication 1756-PM004C-EN-P - October 2009 59
Force I/O Chapter 3
When to Use I/O Force
Use an I/O force to:
• override an input value from another controller (that is, a
consumed tag).
• override an input value from an input device.
• override your logic and specify an output value for another controller
(that is, a produced tag).
• override your logic and specify the state of an output device.
Use these guidelines when forcing an I/O value.
• You can force all I/O data, except for configuration data.
• If the tag is an array or structure, such as an I/O tag, force a BOOL,
SINT, INT, DINT, or REAL element or member.
• If the data value is a SINT, INT, or DINT, you can force the entire value
or you can force individual bits within the value. Individual bits can have
a force status of:
– No force
– Force on
– Force off
• You can also force an alias to an I/O structure member, produced tag,
or consumed tag.
– An alias tag shares the same data value as its base tag, so forcing an
alias tag also forces the associated base tag.
– Removing a force from an alias tag removes the force from the
associated base tag.
• If a produced tag is also Constant, you cannot use forces.
• If a produced tag is forced, you cannot make it Constant.
Forcing increases logic execution time. The more values
you force, the longer it takes to execute the logic.
I/O forces are held by the controller and not by the
programming workstation. Forces remain even if the
programming workstation is disconnected.
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