cat1232 Catalyst Semiconductor, cat1232 Datasheet - Page 6

• Manufacturer Part Number: cat1232
• Description: 5v And 3.3v Supply Monitor, Watchdog Timer, Manual Reset, With Active High & Low Resets
• Manufacturer: Catalyst Semiconductor

CAT1232, CAT1832
WATCHDOG TIMER AND ST
A watchdog timer stops and restarts a microprocessor
that has stopped proper operation or become “hung”.
The watchdog performs this function by monitoring the
ST
input must be strobed with a high-to-low signal
transition prior to the minimum watchdog timeout
period. However if the ST
high-to-low signal transition prior to a watchdog
timeout the reset outputs will become active for TRST
reseting and restarting the microprocessor. Once the
resets return to the inactive state the watchdog timer
restarts the process.
The TD input allows the user to select from three
predetermined watchdog timeout periods. Always use
the minimum timeout period to determine the required
frequency of ST
maximum to determine the time prior to the reset
outputs becoming active. ST
20ns or greater.
The watchdog timer cannot be disabled. It must be
strobed with a high-to-low signal transition to avoid a
watchdog timeout and subsequent reset.
Doc. No. MD-3018 Rev. D
¯¯ input. After the reset outputs go inactive the ST
PBRST
RESET
RESET
Figure 6. Timing Diagram: Pushbutton Reset
¯¯ high-to-low transitions and the
V
IL
t
PDLY
t
PB
1
2
3
4
¯¯ input is not strobed with a
PBRST
TD
TOL
GND
CAT1232LP
Figure 5. CAT1232LP Application Circuit: Watchdog Timer
¯¯ INPUT
¯¯ pulse widths must be
RESET
RESET
V CC
ST
8
7
6
5
V
t
IH
RST
5V
V
V
OH
OL
¯¯
10k ^
6
TD Voltage
Floating
RESET
RESET
RESET
Level
GND
V
Figure 7. Timing Diagram: Strobe Input
Figure 4. CAT1832 Application Circuit:
CC
ST
µP
Note: ST is ignored whenever a reset is active
1
2
3
4
PBRST
TD
TOL
GND
t
RST
CAT1832
Address Bus
Watchdog Time-out Period (ms)
Pushbutton Reset
62.5
MIN
MREQ
250
500
RESET
RESET
V CC
Strobe
Valid
ST
Characteristics subject to change without notice
(Min)
8
7
6
5
t
TD
NOMINAL
t
3.3V
ST
1200
Decoder
Strobe
150
600
Valid
© Catalyst Semiconductor, Inc.
I/O
RESET
(Min)
t
TD
µP
1000
2000
MAX
250
Strobe
Invalid