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Multifunction Module
Digital Input
The 34907A module has two non-isolated 8-bit input/output ports which
you can use for reading digital patterns.
• You can read the live status of the bits on the port or you can
configure a scan to include a digital read.
• You can generate an alarm when a specific bit pattern or bit pattern
change is detected on an input channel. The channels do not have to be
part of the scan list to generate an alarm.
• The internal +5V pull-up circuitry allows you to use the digital input
to detect contact closures like micro-switches or limit switches.
An open input floats to +5V and is read as a “1”. An input shorted to
ground is read as a “0”. An example of a contact closure detection
channel is shown below.
Digital Read
Limit Switch
I/O Line (1 of 8)
+5 V
10 kΩ
+TTL
Reference
(+2.1 V)
–
+
Chapter 8 Tutorial
Multifunction Module
392