µP Reset Circuits with Long Manual Reset

Setup Period

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7

Applications Information

Interrupt Before Reset

To minimize data loss and speed system recovery,

many applications interrupt the processor or reset only

portions of the system before a processor hard reset is

asserted. The extended setup time of the MAX6443–

MAX6452 manual reset inputs allows the same push-

button (connected to both the processor interrupt and

the extended MR1 input, as shown in Figure 6) to con-

trol both the interrupt and hard reset functions. If the

only interrupted. If the system still does not respond

properly, the pushbutton (or two buttons for the dual

manual reset) can be closed for the full extended setup

period to hard reset the processor. If desired, connect

an LED to the RESET output to blink off (or on) for the

reset timeout period to signify when the pushbutton is

closed long enough for a hard reset (the same LED

might be used as the front-panel power-on display).

Smart Card Insertion/Removal

The MAX6447/MAX6448/MAX6451/MAX6452 dual manu-

al resets are useful in applications in which both an

extended and immediate setup periods are needed.

Figure 7 illustrates the insertion and removal of a smart

card. MR1 monitors a front-panel pushbutton. When

50k

Ω resistor, the front-panel switch can be connected to

MR2

RESET

t = 210ms

t < 210ms

COUNTER RESET

Figure 3. MAX6447/MAX6448/MAX6451/MAX6452 MR2

Assertion DebouncingTiming Diagram

MR2

RESET

210ms

DEBOUNCING PERIOD

210ms

TIMEOUT PERIOD

POSITIVE EDGE

NO RESET

OUTPUT

ASSERTED

Figure 4. MAX6447/MAX6448/MAX6451/MAX6452 MR2

Deassertion Debouncing Timing Diagram

MAX6449

MAX6451

RSTIN

R1

R2

RESET

GND

Figure 5. Calculating the Monitored Threshold Voltages

MAX6443L

RESET

+3.3V

NMI

LED

RESET

MR1

GND

PUSHBUTTON SWITCH:

CLOSE FOR < 4.48s

FOR SYSTEM INTERRUPT;

CLOSE FOR > 6.72s FOR

SYSTEM RESET

Figure 6. Interrupt Before Reset Application Circuit