SP691ACN SIPEX [Sipex Corporation], SP691ACN Datasheet - Page 12

• Manufacturer Part Number: SP691ACN
• Description: Low Power Microprocessor Supervisory with Battery Switch-Over
• Manufacturer: SIPEX [Sipex Corporation]

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.
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.
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.
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 V
reset threshold or when WDI is an open circuit.
In watchdog mode, if no transition occurs at
WDI during the watchdog-timeout period,
Date: 5/25/04
SP691A/693A/800L/800M Low Power Microprocessor Supervisor with Battery Switch-Over © Copyright 2004 Sipex Corporation
RESET
WDO
WDI
CC
t
t
t
1
2
3
= RESET Timeout Period
= Normal Watchdog Timeout Period
= Watchdog Timeout Period Immediately After RESET
is less than the
t
1
t
2
t
1
12
t
3
Figure 21. Selecting Timeout Periods
Normal Watchdog Timeout =
External Oscillator
Normal Watchdog Timeout = 1024 Clock Periods
External Clock
1.6sec Normal Watchdog Timeout
Internal Oscillator
100ms Normal Watchdog Timeout
Internal Oscillator
7
8
7
8
7
8
7
8
OSC
OSC
OSC
OSC
OSC
OSC
OSC
OSC
SEL
IN
SEL
SEL
IN
SEL
IN
IN
600 x C
X
X
X
C
47pF
IN
No Connect
No Connect
No Connect
IN
[ms]