FM812 查看數據表（PDF） - Fairchild Semiconductor
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FM812 Datasheet PDF : 6 Pages
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FM811/812
Circuit Description
Microprocessor Reset
The RESET pin is asserted whenever VCC falls below the
reset threshold voltage or if MR (manual reset) is forced low.
The reset pin remains asserted for a period of 40ms after
VCC has risen above the reset threshold voltage or MR has
returned high. The reset function ensures the microprocessor
is properly reset and powers up into a known condition after
a power failure. RESET will remain valid with VCC as low
as 1.4V.
VCC
VTH
MR
tR
tR
RESET
Interfacing to Bidirectional Reset Pins
The FM811/ FM812 can interface with µPs with
bidirectional reset pins by connecting a 4.7kΩ resistor in
series with the FM811/ FM812 output and the µP reset pin.
RESET Valid to 0V
A resistor can be added from the RESET pin to ground to
ensure the RESET output remains low with VCC down to 0V.
A 100kΩ resistor connected from RESET to ground is
recommended. The size of the resistor should be large
enough to not load the RESET output and small enough to
pull-down any stray leakage currents.
VCC
VCC
VCC
VCC Transients
The FM811/ FM812 are relatively immune to negative-going
VCC glitches below the reset threshold. Typically, a negative-
going transient 125mV below the reset threshold with a
duration of 50ms (25ms for FM81_R/S/T) or less will not
cause an unwanted reset.
Manual Reset Function
Momentarily connecting the Manual Reset input pin (MR) to
GND forces a reset. Typically a Push-button switch is used
in most of the applications to force a manual reset. See
Typical Applications diagram. The reset will remain asserted
as long as MR is held low and for one reset time-out period
(140ms min.) after MR goes high. Note that this input cannot
be driven by a CMOS or TTL logic. This pin should be left
floating if manual reset feature is unused.
FM811
RESET
µP
RESET
100k
4
REV. 1.5.1 7/15/02
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