EM6323/24
Watchdog Input
If the watchdog timer has not been cleared within t
WD
(1.6s typ.), reset asserts. The internal 1.6s timer is
cleared by either a reset pulse or by toggling WDI. While
reset is asserted, the timer remains cleared and does not
count. As soon as reset is released, the timer starts
counting.
If the microcontroller I/O connected to WDI is put in a
high impedance condition, the circuit will detect this
condition as a microcontroller in sleep mode and prevent
its watchdog from timing out. To monitor a high
impedance or a three state condition on WDI, the
watchdog input is internally driven low during the first
15/16 of the watchdog timeout period and high for the
last 1/16 of the watchdog timeout period.
When WDI is left unconnected, this internal driver clears
the 1.6s timer every 1.5s. When WDI is three-stated or
unconnected, the maximum allowable leakage current is
0.5µA.
To minimized the overall system power consumption and
therefore for a minimum watchdog input current leave
WDI low for the majority of the watchdog timeout period,
pulsing it low-high-low once within the first 15/16 of the
watchdog timeout period to reset the watchdog timer. If
WDI is externally driven high for the majority of the
timeout period, up to 35µA can flow into WDI. Meanwhile
when the microcontroller is not in sleep mode, the output
of the microcontroller which drives WDI has to be strong
enough to fight the 35µA.
V
DD
V
DD
RESET
1/16 t
WD
Pullup
WDI
Pullup
OFF
ON
OFF
WDI
15/16 t
WD
Transition
Detector
Watchdog Logic
+ Timer
WDI
Pulldown
ON
OFF
ON
t
POR
15/16 t
WD
t
WD
1/16 t
WD
GND
Pulldown
Fig. 15
Fig. 16
WDI Input Timing Diagram
WDI Input Stage Block Schematic
15.0
12.0
9.0
[ uA ]
6.0
3.0
0.0
-50
25.0
20.0
15.0
[ uA ]
10.0
5.0
0.0
-25
0
25
50
75
100
125
-50
-25
0
25
50
75
100 125
[ °C ]
Fig. 17
[ °C ]
Fig. 18
WDI Input Current Low-level I
IL
vs. Temperature
(V
DD
=5.5V)
WDI Input Current High-Level I
IH
vs. Temperature
(V
DD
=5.5V)
Copyright
©
2006, EM Microelectronic-Marin SA
03/06 - rev.H
9
www.emmicroelectronic.com
EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
