Datasheet

Watchdog Software Considerations
One way to help the watchdog timer monitor software
execution more closely is to set and clear the watch-
dog input at different points in the program, rather
than pulsing the watchdog input high-low-high or low-
high-low. This technique avoids a stuck loop, in which the
watchdog timer would continue to be cleared inside the
loop, keeping the watchdog from timing out.
Figure 4 shows an example of a flow diagram where
the I/O driving the watchdog input is set high at the
beginning of the program, set low at the beginning of
every subroutine or loop, then set high again when the
program returns to the beginning. If the program should
hang in any subroutine, the problem would quickly be
corrected, since the I/O is continually set low and the
watchdog timer is allowed to time out, causing an interrupt
to be issued. This scheme results in higher time average
WDI input current than does leaving WDI low for the
majority of the timeout period and periodically pulsing it
low-high-low (see the Watchdog Input Current section).
Figure 4. Watchdog Flow Diagram
Figure 3. Watchdog Timing Relationship
Figure 2. Power-Up Timing Diagram
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
5 SC70 X5+1 21-0076 90-0188
START
SET WDI
HIGH
PROGRAM
CODE
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
RETURN
V
CC
t
WD
t
PP
t
PP
V
UVLO
WDI
WDO
V
CC
V
UVLO
V
UVLO
WDO
t
PP
MAX6814 5-Pin Watchdog Timer Circuit
www.maximintegrated.com
Maxim Integrated │ 5
Chip Information
TRANSISTOR COUNT: 607
PROCESS: BiCMOS
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.