Using Iso Input 5 As A Latch; General-Purpose I/O - National Instruments PCI-8254R User Manual

Based on the input to the product selection port, you can configure the
application software to run the appropriate inspection sequence. For
example, an upstream NI 8254R programmed for part classification might
drive the product selection port of a downstream NI 8254R. Alternatively,
a PLC with information about which part is being inspected can drive the
product selection port of the NI 8254R.

Using ISO Input 5 as a Latch

You can configure the product selection port to use ISO Input 5 as a latch.
A rising edge on ISO Input 5 can latch the data into a data register on the
NI 8254R. Before each inspection, the software checks the status of the
product select inputs and reads the most recent value latched into the
register. If ISO Input 5 is not used as a latch, it can be used as an extra bit
of data.
Note In Vision Builder AI, ISO Input 5 is always designated as a latch.
Table 2-3 lists the product selection ports.
Function
Data(5), rising edge latch
Data(4)
Data(3)
Data(2)
Data(1)
Data(0)

General-Purpose I/O

General-purpose inputs and outputs are available as both TTL and isolated
connections. The software running on the NI 8254R can read the inputs and
drive the outputs high or low at any time.
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Table 2-3. NI 8254R Product Selection Ports
2-9
Chapter 2 Hardware Overview
External Connection
ISO Input 5
ISO Input 4
ISO Input 3
ISO Input 2
ISO Input 1
ISO Input 0
NI PCI-8254R User Manual