Rockwell Automation Logix5000 Controllers I/O and Tag Data Programming Manual - Manual (Page 58)

Chapter 3 Force I/O
Use an I/O force to override:
• An input value from another controller (that is, a consumed tag).
• An input value from an input device.
• Your logic and specify an output value for another controller (that is, a
produced tag).
• Your logic and specify the state of an output device.
Important: • 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.
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, you can 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.
When to use I/O force
58 Rockwell Automation Publication 1756-PM004E-EN-P - October 2014