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???
12/17/06 04:55
Modified:
  12/17/06 05:07
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 		 #129624 - Pull-ups
Responding to: ???'s previous message
Neil said:
They maay have been required bacck then??

Not more required than today: When external memory is addressed by Port0 of 8751H, strong internal active pull-ups are activated. So, at least the addressing of external memory should work without the pull-up resistors.

Nevertheless, when not addressing external memory, Port0 lines can float and potentials can go to the nowhere's land. So, to the Port0 lines connected CMOS latches (or gates), not containing the typical TTL-ish internal pull-up can even oscillate, because of the floating of potential. Because of this and to enhance the noise immunity due to lowered line impedances, I do use 10k pull-up arrays for all the Port lines of micro, not only for the Port0 lines.

Kai

List of 45 messages in thread
TopicAuthorDate
Why would the OLD part get hot?            01/01/70 00:00      
   Could be            01/01/70 00:00      
      just to focus ...            01/01/70 00:00      
         Current consumption?            01/01/70 00:00      
      HMOS            01/01/70 00:00      
         Yes, they were warm ...            01/01/70 00:00      
            some special mode?            01/01/70 00:00      
               I know            01/01/70 00:00      
               I doubt there\'s a special mode involved            01/01/70 00:00      
                  BI NGO!            01/01/70 00:00      
                     Not yet, my friend ... but you\'re onto something            01/01/70 00:00      
                        doen memory lane            01/01/70 00:00      
                           it's all pretty confusing            01/01/70 00:00      
                              they all did            01/01/70 00:00      
   well ... the REAL question is ...            01/01/70 00:00      
   Have you tried using slow SRAM...            01/01/70 00:00      
      How about....            01/01/70 00:00      
         I'm not sure what that will tell me.            01/01/70 00:00      
      What do you believe that would do?            01/01/70 00:00      
         Step Back            01/01/70 00:00      
            Well, that's how it is ...            01/01/70 00:00      
   Some hints            01/01/70 00:00      
      Yes, that\'s so ...            01/01/70 00:00      
         Maybe            01/01/70 00:00      
            Intel doesn\'t care ...            01/01/70 00:00      
            O.K. ... so here\'s what I\'ve found ...            01/01/70 00:00      
               do you want to be stylish?            01/01/70 00:00      
                  Bipolar logic? Maybe            01/01/70 00:00      
                     Back in the day            01/01/70 00:00      
                        Pull-ups            01/01/70 00:00      
                           Dynamic logic may be the reason for the hot part            01/01/70 00:00      
                           That's what I find confusing            01/01/70 00:00      
                              pullups HCT and LS            01/01/70 00:00      
                                 74HCTMOS does not contain internal pull-ups            01/01/70 00:00      
                                 emitters vs resistors            01/01/70 00:00      
                           So, Kai, How did you arrive at 10K-ohms?            01/01/70 00:00      
                              No calculations, just a compromise            01/01/70 00:00      
                                 I haven't tried it with LS parts ... yet ...            01/01/70 00:00      
                                    throw away that databook :-)            01/01/70 00:00      
                                       Well, it's the old TTL book from TI ...            01/01/70 00:00      
                                          just a thought re LS pullup            01/01/70 00:00      
                                             That's the HCTLS from Samsung            01/01/70 00:00      
                        re: back in the day            01/01/70 00:00      
                           What about P2?            01/01/70 00:00      
                              No Just P0            01/01/70 00:00      

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