October 2006
rev 1.6
ASM1832
signals. The pushbutton input is debounced and is pulled
minimum timeout period, reset signals become active. On
power-up after the supply voltage returns to an in-tolerance
condition, the reset signal remains active for 250ms
minimum, allowing the power supply and system
microprocessor to stabilize.
HIGH through an internal 40kΩ resistor.
When PBRST is held LOW for the minimum time tPB, both
resets become active and remain active for a minimum time
period of 250ms after PBRST returns HIGH.
ST Pulses as short as 20ns can be detected.
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.
Valid
Strobe
Valid
Strobe
Invalid
Strobe
ST
tST
tRST
The PBRST can be driven from a TTL or CMOS logic line or
shorted to ground with a mechanical switch.
tTD (min)
tTD (max)
RESET
t
PB
Note: ST is ignored whenever a reset is active
PBRST
Figure 5: Timing Diagram: Strobe Input
V
IH
t
PDLY
Timeouts periods of approximately 150ms, 610ms or
1,200ms are selected through the TD pin.
V
IL
t
RST
Watchdog Time-out Period
TD Voltage level
(ms)
RESET
RESET
VOH
VOL
Min
Nom
Max
GND
Floating
VCC
62.5
250
500
150
610
250
1000
2000
Figure 3: Timing Diagram: Pushbutton Reset
1200
Supply
Voltage
The watchdog timer can not be disabled. It must be strobed
with a high-to-low transition to avoid watchdog timeout and
reset.
ASM1832
1
2
8
7
V
CC
PBRST
T
D
I/O
ST
µP
3
4
6
Supply
Voltage
TOL
RESET
5
GND RESET
RESET
ASM1832
MREQ
1
2
8
7
V
CC
PBRST
Figure 4: Application Circuit: Pushbutton Reset
T
D
ST
µP
Decoder
3
4
6
Watchdog Timer and ST Input
TOL
RESET
RESET
Address
Bus
RESET
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
5
GND
Figure 6: Application Circuit: Watchdog Timer
3.3V µP Power Supply Monitor and Reset Circuit
4 of 9
Notice: The information in this document is subject to change without notice
PULSECORE [ PulseCore Semiconductor ]
