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MAX6446UK46L Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX6446UK46L Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 13 page µP Reset Circuits with Long Manual Reset Setup Period _______________________________________________________________________________________ 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 pushbutton is closed for less than tMR, the processor is 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 closed for tMR, RESET one-shot pulses low for 140ms min. Because MR1 is internally pulled to VCC through a 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 VCC R1 R2 RESET GND VMON_TH = 0.63 x (R1 + R2) / R2 VMON_TH VCC Figure 5. Calculating the Monitored Threshold Voltages MAX6443L µP VCC RESET VCC +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 |
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