I/O Addressing - Allen-Bradley MicroLogix 1400 Instruction Manual

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I/O Forcing
Input Filtering
I/O forcing is the ability to override the actual status of the I/O at the
user's discretion.
Input Forcing
When an input is forced, the value in the input data file is set to a
user-defined state. For discrete inputs, you can force an input "on" or
"off". When an input is forced, it no longer reflects the state of the
physical input or the input LCD indicator. For embedded inputs, the
controller reacts as if the force is applied to the physical input terminal.
When an input is forced, it has no effect on the input device connected to
TIP
the controller.
Output Forcing
When an output is forced, the controller overrides the status of the control
program, and sets the output to the user-defined state. Discrete outputs
can be forced "on" or "off". The value in the output file is unaffected by
the force. It maintains the state determined by the logic in the control
program. However, the state of the physical output and the output LCD
indicator will be set to the forced state.
If you force an output controlled by an executing PTOX or PWMX function,
TIP
an instruction error is generated.
The MicroLogix 1400 controllers allow users to configure groups of DC
inputs for high-speed or normal operation. Users can configure each input
group's response time. A configurable filter determines how long the
input signal must be "on" or "off" before the controller recognizes the
signal. The higher the value, the longer it takes for the input state to be
recognized by the controller. Higher values provide more filtering, and
are used in electrically noisy environments. Lower values provide less
filtering, and are used to detect fast or narrow pulses. The filters can be
set to a lower value when using high-speed counters, latching inputs, and
input interrupts.
I/O Configuration
Publication 1766-RM001A-EN-P - October 2008
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