ASM1232LPS Alliance Semiconductor, ASM1232LPS Datasheet - Page 4

• Manufacturer Part Number: ASM1232LPS
• Description: 5V uP Power Supply Monitor and Reset Circuit
• Manufacturer: Alliance Semiconductor

January 2005
rev 1.5
When PBRST is held LOW for the minimum time t
resets become active and remain active for a minimum time
period of 250ms after PBRST returns HIGH.
The debounced input is guaranteed to recognize pulses
greater than 20ms. No external pull-up resistor is required,
since PBRST is pulled HIGH by an internal 40kΩ resistor.
The PBRST can be driven from a TTL or CMOS logic line or
shorted to ground with a mechanical switch.
Watchdog Timer and ST Input
A watchdog timer stops and restarts a microprocessor that is
“hung-up”. The µP must toggle the ST input within a set
period (as selectable through TD input) to verify proper
software execution. If the ST is not toggled low within the
minimum timeout period, reset signals become active. In
Figure 3: Timing Diagram: Pushbutton Reset
PBRST
RESET
RESET
Figure 4: Application Circuit: Pushbutton Reset
1
2
4
3
ASM1232LP/LPS
GND
PBRST
TD
TOL
V
t
PDLY
IL
RESET
RESET
V
ST
CC
t
PB
5
6
7
8
5V
Notice: The information in this document is subject to change without notice
5V µP Power Supply Monitor and Reset Circuit
I/O
RESET
t
V
RST
IH
µP
PB
V
V
OH
OL
, both
power-up after the supply voltage returns to an in-tolerance
condition, the reset signal remains active for 250ms
minimum,
microprocessor to stabilize. ST pulses as short as 20ns can
be detected.
Timeouts periods of approximately 150ms, 610ms or
1,200ms are selected through the TD pin.
The watchdog timer can not be disabled. It must be strobed
with a high-to-low transition to avoid watchdog timeout and
reset.
Note: ST is ignored whenever a reset is active
Figure 5: Timing Diagram: Strobe Input
GND
Floating
V
CC
Figure 6: Application Circuit: Watchdog Timer
TD Voltage level
RESET
ST
1
2
4
3
ASM1232 LP/LPS
allowing
t
GND
PBRST
T
TOL
RST
D
RESET
V
ST
Valid
Strobe
CC
the
t
t
TD
ST
5
6
7
8
5V
(min)
power
ASM1232LP/LPS
Watchdog Time-out Period
62.5
Min
250
500
Valid
Strobe
10kΩ
supply
RESET
t
TD
µP
(ms)
(max)
Nom
1200
150
610
Address
MREQ
and
Bus
Invalid
Strobe
1000
2000
system
Decoder
4 of 10
Max
250