National Instruments NI PCIe-8255R User Manual

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National Instruments NI PCIe-8255R User Manual Manual pdf 24 page image

Chapter 2 Hardware OverviewNI PCIe-8255R User Manual 2-12 ni.comNote For prototyping when equipment is unavailable, you can wire from V iso toISO Input 11 to simulate external equipment that indicates to the NI 8255R to operatenormally.Watchdog TimerThe watchdog timer is a software configurable feature that can monitorsoftware on the NI 8255R and take action if the software is unresponsive.The millisecond counter on the watchdog timer is configurable up to65,534 ms, in 1 ms increments, before it expires.Configure the watchdog timer to take one of the following actions when itexpires.Caution Use the Indicator Only option only to test the watchdog timer. If softwarebecomes unresponsive, it cannot be relied upon to send notification to the host.• Indicator Only—This option sends the expiration signal back to thedevelopment machine through software. True indicates an expiredwatchdog timer. False indicates an unexpired watchdog timer. Theexpiration signal that indicates an expired watchdog timer continues toassert until the watchdog timer is disarmed. Disarming the watchdogtimer resets the software indicator.• TTL Output 0—This option outputs a signal on TTL Output 0. Highindicates that the watchdog timer has expired. Low indicates that thewatchdog timer has not expired. If the watchdog timer has expired, theexpiration signal continues to assert until the watchdog timer isdisarmed.• Shutdown—If Shutdown mode is enabled, the outputs go to theuser-defined shutdown states.