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???
08/01/06 16:58
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#121502 - there is no reason, but 'linear thinking' (outputs
Responding to: ???'s previous message
Yes, there are often undesirable effects associated with attaching one output to another. It's not advisable practice, but INPUTs to outputs, in this case WEAK pullups, if available, will cause no damaging effects.

There is no reason, but 'linear thinking' (outputs should be push-pull) to configure the keypad outputs as push-pull. The keypad (if reasonably close to the processor) will work equally well with weak pull-up as with push-pull.

Erik

List of 41 messages in thread
TopicAuthorDate
connecting a keypad . HOW?            01/01/70 00:00      
   Because...            01/01/70 00:00      
      How many times will this come up?            01/01/70 00:00      
         To be fair            01/01/70 00:00      
         Help him!            01/01/70 00:00      
            OK ... but just this once!            01/01/70 00:00      
   it's quite simple ... therein lies the beauty.            01/01/70 00:00      
      In minute detail            01/01/70 00:00      
         Credit goes to original author Michael Karas            01/01/70 00:00      
            Yes - Credit to Michael Karas            01/01/70 00:00      
      Diodes prevent \"ghosting\"            01/01/70 00:00      
         indeed, but rarely needed            01/01/70 00:00      
            Think of a piano, where each key counts...            01/01/70 00:00      
               How often do you intend to use multiple keys?            01/01/70 00:00      
                  There is the case of...            01/01/70 00:00      
                     True, but how often?            01/01/70 00:00      
                        Agreed            01/01/70 00:00      
                        general input            01/01/70 00:00      
                  I agree, but...            01/01/70 00:00      
      a small catch            01/01/70 00:00      
         In this case, the pullups were external            01/01/70 00:00      
            HUH????            01/01/70 00:00      
               Sorry, I should have said you must not ...            01/01/70 00:00      
                  just visualize            01/01/70 00:00      
                     It happens all the time ...            01/01/70 00:00      
                        current limits            01/01/70 00:00      
                           transistors open won't conduct            01/01/70 00:00      
                              Totally unsuited with push/pulls, unless...            01/01/70 00:00      
                                 This is true, which is why one should READ first            01/01/70 00:00      
                                    there is no reason, but 'linear thinking' (outputs            01/01/70 00:00      
                                       Some encoders "see" pretty high impedances            01/01/70 00:00      
                                          cruel and unusual            01/01/70 00:00      
                                       No!            01/01/70 00:00      
                                          OK, rephrase            01/01/70 00:00      
                                             Ah, sorry!            01/01/70 00:00      
                                    Benefit of additional pull-ups            01/01/70 00:00      
   Disappearing Original Post!            01/01/70 00:00      
      that is not all that is missing!            01/01/70 00:00      
         Bug            01/01/70 00:00      
            Bugs            01/01/70 00:00      
               OOps            01/01/70 00:00      

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