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???
03/31/08 23:52
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 		 #152809 - I would try this
Responding to: ???'s previous message


At input of circuit a pull-up of 4k7 can be seen. This, because your RTC provides the /IRQ output as open drain.

The time constant of monoflop of about 22msec is formed by a 4k7 resistance and a 4ยต7 capacitance. A tantal can be used, but a ceramic high cap (e.g. X5S) is a better choice.
Parts are relatively low ohmic in order to keep the circuit immune against capacitive stray coupling.

The two 330R resistors are to protect the according gate input, when Vcc is quickly turned off and to protect the micro during power on reset, when the /INT pin might emit low level for a brief period.

Kai

List of 42 messages in thread
TopicAuthorDate
Problem waking up from power down mode:AT89S52            01/01/70 00:00      
   Have you seen the pulse?            01/01/70 00:00      
      Saw tthat            01/01/70 00:00      
         I agree!            01/01/70 00:00      
      monoflop IC number?            01/01/70 00:00      
         also know as one shot (in the foot)            01/01/70 00:00      
            Supervisor chip?            01/01/70 00:00      
               try digikey            01/01/70 00:00      
                  Can you explain how that would help?            01/01/70 00:00      
         how about 4538?            01/01/70 00:00      
         You can, but also read this...            01/01/70 00:00      
      Maybe rather than a monoflop....            01/01/70 00:00      
         Ehem...            01/01/70 00:00      
            Ehem....Hmmm            01/01/70 00:00      
               Why messy?            01/01/70 00:00      
               Remember that the oscillator is turned off            01/01/70 00:00      
                  So using a one-shot seems the best idea..right?            01/01/70 00:00      
                     a one shot should always ...            01/01/70 00:00      
                        I tried using an RC circuit...but it did not work            01/01/70 00:00      
                           sorry, I was wrong            01/01/70 00:00      
                              If one shot is a close second...            01/01/70 00:00      
                                 I'd rather not            01/01/70 00:00      
                                    but problem with FF is that            01/01/70 00:00      
                                       ah, Arghmel            01/01/70 00:00      
                           Not same part            01/01/70 00:00      
                     If You Use PCF8563 RTC...            01/01/70 00:00      
                        555 vs '121? Which is better?            01/01/70 00:00      
                           121 ..            01/01/70 00:00      
                              I used a 74LS121 and...            01/01/70 00:00      
                                 yes it will, but            01/01/70 00:00      
                                    HC and HCT?            01/01/70 00:00      
                                       there is this fancy newfangled thing ....            01/01/70 00:00      
                                    There is no 74HC121, but HC123 and HC221            01/01/70 00:00      
                                 Should really consider....            01/01/70 00:00      
                                    I really would consider PCF8563 but...            01/01/70 00:00      
                           Digital pulse is still better            01/01/70 00:00      
                     I would try this            01/01/70 00:00      
                        elegant, but why ....            01/01/70 00:00      
                           You can, of course, but...            01/01/70 00:00      
                              reg power consumtption...            01/01/70 00:00      
                                 Have you seen my circuit?            01/01/70 00:00      
                                    Pulse Mode from RTC,,,,            01/01/70 00:00      

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