
STM706T/S/R; STM706P; STM708T/S/R
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Pin Descriptions
MR.
A logic low on MR asserts the reset output.
Reset remains asserted as long as MR is low and
for t
rec
after MR returns high. This active-low input
has an internal pull-up. It can be driven from a TTL
or CMOS logic line, or shorted to ground with a
switch. Leave open if unused.
WDI.
If WDI remains high or low for 1.6sec, the in-
ternal watchdog timer runs out and reset (or WDO)
is triggered. The internal watchdog timer clears
while reset is asserted or when WDI sees a rising
or falling edge.
The watchdog function cannot be disabled by al-
lowing the WDI pin to float.
WDO.
WDO goes low when a transition does not
occur on WDI within 1.6sec, and remains low until
a transition occurs on WDI (indicating the watch-
dog interrupt has been serviced). WDO also goes
low when V
CC
falls below the reset threshold; how-
ever, unlike the reset output, WDO goes high as
soon as V
CC
exceeds the reset threshold.
Note:
For those devices with a WDO output, a
watchdog timeout will not trigger reset unless
WDO is connected to MR.
RST.
Pulses low for t
rec
when triggered, and stays
low whenever V
CC
is below the reset threshold or
when MR is a logic low. It remains low for t
rec
after
either V
CC
rises above the reset threshold, the
watchdog triggers a reset, or MR goes from low to
high.
RST.
Pulses high for t
rec
when triggered, and
stays high whenever V
CC
is above the reset
threshold or when MR is a logic high. It remains
high for t
rec
after either V
CC
falls below the reset
threshold, the watchdog triggers a reset, or MR
goes from high to low.
PFI.
When PFI is less than V
PFI
, PFO goes low;
otherwise, PFO remains high. Connect to ground
if unused.
PFO.
When PFI is less than V
PFI
, PFO goes low;
otherwise, PFO remains high. Leave open if un-
used.
Table 3. Pin Description
Pin
Name
Function
STM706P
STM706T/S/R
STM708T/S/R
SO8
TSSOP8
SO8
TSSOP8
SO8
TSSOP8
1
3
1
3
1
3
MR
Push-button Reset Input
6
8
6
8
–
–
WDI
Watchdog Input
8
2
8
2
–
–
WDO
Watchdog Output
–
–
7
1
7
1
RST
Active-Low Reset Output
7
1
–
–
8
2
RST
Active-High Reset Output
2
4
2
4
2
4
V
CC
Supply Voltage
4
6
4
6
4
6
PFI
PFI Power-fail Input
5
7
5
7
5
7
PFO
PFO Power-fail Output
3
5
3
5
3
5
V
SS
Ground
–
–
–
–
6
8
NC
No Connect