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???
04/24/08 18:58
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 		 #153981 - This thread turns to helter-skelter
Responding to: ???'s previous message
P. said:
As port0 is defined as databus(D0-D7) which can be connected to multiple devices like RAM, ROM etc the port should be tristate. With internal pullup(FET Circuit) this is not possible.

Of course, it is! Turn-off the n-FET and the active pull-up providing p-FETs and you have a decent tri-state. That's exactly how the 8051 and nearly all other digital chips work.

Kai

List of 33 messages in thread
TopicAuthorDate
about port 0 0f 8051mc            01/01/70 00:00      
   already answered            01/01/70 00:00      
      P0 pullups            01/01/70 00:00      
         Tristate (pedant mode)            01/01/70 00:00      
         This thread turns to helter-skelter            01/01/70 00:00      
         I never heard of that            01/01/70 00:00      
            I never heard of that ?            01/01/70 00:00      
            I never heard of that ?            01/01/70 00:00      
               Tristate (pedant mode, again)            01/01/70 00:00      
                  three states            01/01/70 00:00      
                     not at all confusing            01/01/70 00:00      
               confusing open drain/collector with tristate ...            01/01/70 00:00      
                  Not quite true            01/01/70 00:00      
                     much 'can' be done            01/01/70 00:00      
   read the datasheet ... it is "open-drain"            01/01/70 00:00      
      advantage            01/01/70 00:00      
         that it is not clogged            01/01/70 00:00      
            or a wire-or-ed output            01/01/70 00:00      
               ????            01/01/70 00:00      
         How would you realize an input /output topology?            01/01/70 00:00      
            why            01/01/70 00:00      
               this is the diagram of the "inside" of chip            01/01/70 00:00      
            please comment            01/01/70 00:00      
               1) Maybe, 2) False, 3) False            01/01/70 00:00      
               FAQ            01/01/70 00:00      
               Have you read at all what I wrote??            01/01/70 00:00      
   Port 0            01/01/70 00:00      
      Hhm, still no answer??            01/01/70 00:00      
         This doc explained everything            01/01/70 00:00      
            it should be the first reference!            01/01/70 00:00      
      P0.1            01/01/70 00:00      
         start a new thread            01/01/70 00:00      
         yes to both - it\'s \"bible time\"            01/01/70 00:00      

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