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6.4
SUPERVISION FEATURES
6.4.1 WATCHDOG
The PCI-934 provides a two-stage watchdog to monitor the CPU inactivity. The function of
the watchdog is to generate a failure signal if the processor is not able to generate a 0-1-0 data
toggle for longer than the watchdog timeout period. The feature is useful in embedded
systems where human supervision is not required or impossible.
The watchdog configuration may be selected between Dual-Stage, Single-Stage, or disabled,
using the W6 jumper (see Section11 – Setting Jumpers).
The default timeout period is 1.6 seconds for each stage; however, the timeout period can
be changed. Shorting C380/C353 and leaving R249/R230 opened changes the timeout to
100ms. Shorting the resistor and installing a capacitor will change the timeout period of the
watchdog according to the following formula:
Timeout (milliseconds) =
For instance, an external capacity of 100pF will lengthen the watchdog timeout to 851ms
and a 1000pF will bring it to 8.5 seconds.
CAUTION
Modifying the Watchdog timeout period will also modify the value of
the Reset period according to the following formula:
400ms
or
xC
47pF
(200ms/47pF) x C
6-7
Installing and Working with System Components
Timeout (ms) x 47pF
C =
400ms
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