MAX808N Maxim Integrated Products, MAX808N Datasheet - Page 12

• Manufacturer Part Number: MAX808N
• Description: (MAX801x / MAX808x) Supervisory Circuits
• Manufacturer: Maxim Integrated Products

To help the watchdog timer keep a closer watch on
software execution, you can set and reset 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, where the
watchdog timer continues to be reset within the loop,
keeping the watchdog from timing out.
Figure 9 shows a sample flow diagram where the I/O
driving the watchdog input is set high at the beginning
of the program, low at the beginning of every subrou-
tine or loop, then high again when the program returns
to the beginning. If the program should “hang” in any
subroutine, the I/O would be continually set low and the
watchdog timer would be allowed to time out, causing a
reset or interrupt to be issued.
The V
the battery switchover comparator and should not
exceed 0.03V/µs. A standard rule for filter capacitance
on most regulators is around 100µF per Ampere of cur-
rent. When the power supply is shut off or the main bat-
tery is disconnected, the associated initial V
is just the inverse, or 1A/100µF = 0.01V/µs.
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 [phone]
© 1996 Maxim Integrated Products
8-Pin µP Supervisory Circuits
with ±1.5% Reset Accuracy
_________________Pin Configurations
CC
TOP VIEW
fall time is limited by the propagation delay of
Watchdog Software Considerations
LOWLINE
LOWLINE
RESET
RESET
GND
GND
V
V
CC
CC
1
2
3
4
1
2
3
4
DIP/SO
DIP/SO
Maximum V
MAX808
MAX801
8
7
6
5
8
7
6
5
OUT
BATT
CE IN
CE OUT
OUT
BATT
WDI
RESET
Printed USA
CC
Fall Time
CC
fall rate
Figure 9. Watchdog Flow Diagram
TRANSISTOR COUNT: 922
___________________Chip Information
is a registered trademark of Maxim Integrated Products.
OR PROGRAM LOOP,
SUBROUTINE
SET WDI
RETURN
START
HIGH
LOW
END
WDI
SET