MAX6854 MAXIM [Maxim Integrated Products], MAX6854 Datasheet - Page 13

• Manufacturer Part Number: MAX6854
• Description: Nanopower uP Supervisory Circuits with Manual Reset and Watchdog Timer
• Manufacturer: MAXIM [Maxim Integrated Products]

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 reset inside the
loop, keeping the watchdog from timing out.
Figure
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
a reset or interrupt to be issued.
Figure
6. Watchdog Flow Diagram
6 shows an example of a flow diagram where
Nanopower µP Supervisory Circuits with
______________________________________________________________________________________
SUBROUTINE OR
PROGRAM LOOP
SET WDI LOW
PROGRAM
SET WDI
RETURN
START
CODE
HIGH
Manual Reset and Watchdog Timer
Table
Table
SUFFIX
SUFFIX
225
46
45
44
43
42
41
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
S
L
2. Threshold Suffix Guide
3. Watchdog Timeout
4.509
4.388
4.266
4.193
4.095
3.998
3.900
3.802
3.705
3.608
3.510
3.413
3.315
3.218
3.120
2.998
2.925
2.852
2.730
2.633
2.559
2.438
2.340
2.255
2.180
2.133
2.048
1.950
1.853
1.755
1.623
1.536
MIN
MIN
1.5
95
V
CC
WATCHDOG TIMEOUT PERIOD
THRESHOLD FALLING
4.625
4.500
4.375
4.300
4.200
4.100
4.000
3.900
3.800
3.700
3.600
3.500
3.400
3.300
3.200
3.075
3.000
2.925
2.800
2.700
2.625
2.500
2.400
2.313
2.235
2.188
2.100
2.000
1.900
1.800
1.665
1.575
TYP
TYP
209
3.3
4.741
4.613
4.484
4.408
4.305
4.203
4.100
3.998
3.895
3.793
3.690
3.588
3.485
3.383
3.280
3.152
3.075
2.998
2.870
2.768
2.691
2.563
2.460
2.371
2.290
2.243
2.153
2.050
1.948
1.845
1.707
1.614
MAX
MAX
7.75
487
UNITS
UNITS
V
s
13