Continuum I/O System Reference
31
Sensing Digital Inputs or Contact Closures
Digital input points are designed to allow the monitoring of logic level signals or contact
closures across an input (contact wired between the input and return).
•
When monitoring a digital logic level signal, the pull-up resistor must be disabled (set
to OFF).
•
To sense a contact closure, the pull-up resistor must be enabled (set to ON).
To sense a digital input or contact closure, configure an input point with an Electrical
Type of
Digital
.
A digital input is considered “ON” whenever the voltage across its input meets or exceeds
the ON Threshold. For a contact closure, this is 0 (zero) volts. Similarly, an OFF condition
meets, or is lower than, the Off Threshold. With a contact closure, this is the value of
Vref.
Note
: When configuring a Digital point, there is a ‘Polarity’ attribute. If this attribute is
enabled, readings are reversed: ‘On’ will occur when the input is at Vref because the
contact is open, and ‘Off’ occurs when the input is at 0 volts because the contact is
closed.
IN x
RET
Contact
Closure
UI-8-10
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