National Instruments NI PCI-8254R - Manual (Page 21)

Chapter 2 Digital I/O
NI PCI-8254R User Manual 2-10 ni.com
An example of how to use general-purpose inputs is reading the status of a
general-purpose input as the first step in your inspection sequence and
recording that value as part of your inspection.
General-Purpose Outputs
The primary difference between general-purpose outputs and timed pulse
outputs is that the timing of general-purpose outputs is controlled by
software rather than hardware. As a result, timing of general-purpose
outputs changes as the inspection algorithm changes, which makes
general-purpose outputs less appropriate than timed outputs for camera
control, strobe light control, and other applications that require precise
timing.
An example of using general-purpose outputs is driving a relay that turns
on an Inspection in Progress light for an operator to see while the
inspection sequence is running.
I/O for Fault Conditions
The NI 8254R recognizes the following fault conditions:
• External shutdown, when Shutdown mode is enabled
• Watchdog timer expiration
In the event of a fault condition, the behavior of the NI 8254R is dependent
on configuration settings of the software-enabled Shutdown mode. To
resume operation, address the fault condition and cycle power on your
computer.
Table 2-4 summarizes how user configuration affects the behavior of the
NI 8254R in the event of a fault condition.
The following sections describe each fault condition.
Table 2-4. Fault Condition Behavior
Fault Condition Shutdown Enabled
Outputs Change to
User-Defined States
External Shutdown On
Off
Yes
No
Watchdog On
Off
Yes
No