National Instruments NI PCI-8254R Using ISO Input 5 as a Latch, General-Purpose I/O, General-Purpose Inputs

Chapter 2 Digital I/O

example, an upstream NI 8254R device programmed for part classification

might drive the product selection port of a downstream NI 8254R device.

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

of data.

Note In Vision Builder AI, ISO Input 5 is always designated as a latch.

Table2-3 lists the product selection ports.

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.

General-Purpose Inputs

The primary difference between general-purpose inputs and trigger inputs

is that you cannot use general-purpose inputs to initiate a timed pulse

generator. In an application, use the general-purpose inputs to get the status

of the inputs at a given point and not to synchronize the NI 8254R with an

external event.

Table 2-3. NI 8254R Product Selection Ports

Function External Connection

Data(5), rising edge latch ISO Input 5

Data(4) ISO Input 4

Data(3) ISO Input 3

Data(2) ISO Input 2

Data(1) ISO Input 1

Data(0) ISO Input 0