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Chapter 2 Hardware Overview
© National Instruments Corporation 2-11 NI PCI-8254R User Manual
The following sections describe each fault condition.
Shutdown
Shutdown mode is a software-enabled feature that, when activated, allows
an external device to halt the NI 8254R processing operations.
Additionally, Shutdown mode allows you to specify user-defined
shutdown states for all fault conditions.
When Shutdown mode is enabled and the shutdown input signal,
ISO Input 11, turns off, the NI 8254R registers an external shutdown
condition. When a fault occurs, outputs operate according to user-defined
shutdown states. Each TTL output is configurable to drive high, drive low,
or tri-state, and each isolated output is on/off configurable.
Note For prototyping when equipment is unavailable, you can wire from V to
ISO Input 11 to simulate external equipment that indicates to the NI 8254R to operate
normally.
Watchdog Timer
The watchdog timer is a software configurable feature that can monitor
software on the NI 8254R and take action if the software is unresponsive.
The millisecond counter on the watchdog timer is configurable up to
65,534 ms, in 1 ms increments, before it expires.
Configure the watchdog timer to take one of the following actions when it
expires.
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