Pulse Catch Bits Tab - System Block Configuration
View the System Block to set up PLC options by using one of the following methods:
·Click the System Block button on the Navigation Bar.
·Select the View > System Block menu command.
·Click on the System Block icon in the Instruction Tree.
Click on the Pulse Catch Bits tab to set digital input properties. Edit the properties and then download the modifications to the PLC.
The pulse catch feature allows you to capture high-going pulses or low-going pulses that are of such a short duration that they would not always be seen when the PLC reads the digital inputs at the beginning of the scan cycle.
The maximum number of digital inputs for which this feature can be used is dependent on the PLC model:
·CPU 221 maximum is 6 digital inputs
·CPU 222 maximum is 8 digital inputs
·CPU 224, CPU 226, and CPU 226XM maximum is 14 digital inputs
The pulse catch feature is not available for CPU 21x models.
Pulse catch operation can be individually enabled on each of the local digital inputs. When pulse catch is enabled for an input, a change in state of the input is latched and held until the next input cycle update. In this way a pulse that lasts for a short period of time is caught and held until the PLC reads the inputs, assuring you that the pulse will not be missed. The basic operation of the PLC with and without pulse catch enabled is shown below.
When using the pulse catch function, you must be sure to adjust the input filter time so that the pulse is not removed by the filter. (The pulse catch function operates on the input after it passes through the input filter.)
Application User Reference
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