SP691A Datasheet, PDF (12/24 Pages) Sipex Corporation – Low Power Microprocessor Supervisory with Battery Switch-Over

WDI
WDO
t2
RESET
t3
t1
t1
t1 = RESET Timeout Period
t2 = Normal Watchdog Timeout Period
t3 = Watchdog Timeout Period Immediately After RESET
Figure 20. Watchdog Timeout Period and Reset Active Time
Watchdog Function
The watchdog monitors µP activity via the
Watchdog Input (WDI). If the µP becomes
inactive, RESET and RESET are asserted.
To use the watchdog function, connect WDI to
a bus line or µP I/O line. If WDI remains high
or low for longer than the watchdog timeout pe-
riod (1.6s nominal). WDO, RESET, and RESET
are asserted, indicating a software fault or idle
conditions. Refer to RESET and RESET
Outputs and Watchdog Output sections.
OSCIN
7
X No Connect
8 ^OSCSEL X No Connect
1.6sec Normal Watchdog Timeout
Internal Oscillator
OSCIN
7
Watchdog Input
A change of logic state (minimum 100ns
duration) at WDI during the watchdog period
will reset the watchdog timer. The watchdog
default timout is 1.6sec.
8 ^OSCSEL X No Connect
100ms Normal Watchdog Timeout
Internal Oscillator
To disable the watchdog function, leave WDI
floating. An internal resistor network (100kΩ
equivalent impedance at WDI) biases WDI to
approximately 1.6V. Internal comparators
detect this level and disable the watchdog timer.
When Vcc is below the reset threshold, the
watchdog function is disabled and WDI is
disconnected from its internal resistor network,
thus becoming high impedance.
CIN
OSCIN
7
8 ^OSCSEL
Normal Watchdog Timeout
External Oscillator
=
600 x CIN
47pF
[ms]
Watchdog Output
WDO remains high if there is activity (transition
or pulse) at WDI during the watchdog-timeout
period. The watchdog function is disabled and
WDO is a logic high when VCC is less than the
reset threshold or when WDI is an open circuit.
In watchdog mode, if no transition occurs at
WDI during the watchdog-timeout period,
OSCIN
7
8 ^OSCSEL
Normal Watchdog Timeout = 1024 Clock Periods
External Clock
Figure 21. Selecting Timeout Periods
Date: 5/25/04
SP691A/693A/800L/800M Low Power Microprocessor Supervisor with Battery Switch-Over © Copyright 2004 Sipex Corporation
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