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FM811SUX Datasheet(PDF) 4 Page - Fairchild Semiconductor |
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FM811SUX Datasheet(HTML) 4 Page - Fairchild Semiconductor |
4 / 6 page FM811/812 4 REV. 1.5.1 7/15/02 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 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. Interfacing to Bidirectional Reset Pins The FM811/ FM812 can interface with µPs with bidirectional reset pins by connecting a 4.7k Ω 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 100k Ω 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. VTH VCC tR MR RESET tR FM811 µP 100k VCC VCC RESET RESET VCC |
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Similar Description - FM811SUX |
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