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???
05/27/05 11:55
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 		 #93974 - PSEN III.
Responding to: ???'s previous message
So if datasheets are unclear, it's time to go real.
AT89S8252, executing from internal FLASH this stupid loop:
Save This Code
loop:
   mov  dptr,#0AA55h
   movc a,@a+dptr
   ljmp loop
The result is here (the two waveforms are not taken simultaneously, so they may be skewed to each other), for /PSEN and a P2 pin, both pulled down by 22k resistors:



Clearly, /PSEN is push/pull - exactly as Oleg said. However, the datasheet would suggest that /PSEN has the same structure as P1,P2,P3 (the same VOH). As it states minimum limit for VOH (2.4V at 60uA - and the pullup draws around 220uA, while VOH on PSEN is obviously still around 5V...) so this is formally OK, but still I think rather confusing...

I also tried an intel 8752, with the following result:



Here, /PSEN has a weaker "1" transistor (22k pulls down to 4V) but still seems to be push-pull - except while in RESET...


Jan Waclawek


List of 30 messages in thread
TopicAuthorDate
Free PSEN/EA            01/01/70 00:00      
   Need 2 extra I/O?            01/01/70 00:00      
   Break            01/01/70 00:00      
      Just like disabling ALE            01/01/70 00:00      
         EA is a problem; PSEN - I don't know            01/01/70 00:00      
            Undocumented features            01/01/70 00:00      
               this is a weak argument            01/01/70 00:00      
            PSEN            01/01/70 00:00      
               PSEN II.            01/01/70 00:00      
                  PSEN III.            01/01/70 00:00      
            More I/O            01/01/70 00:00      
               I don't think that was Payam's point            01/01/70 00:00      
   the never ending request            01/01/70 00:00      
      ;-)            01/01/70 00:00      
   You can use ALE            01/01/70 00:00      
      Filter?            01/01/70 00:00      
         I assume ..            01/01/70 00:00      
            dirty hack...            01/01/70 00:00      
               why hack            01/01/70 00:00      
                  extra IO            01/01/70 00:00      
                     design and nothing else            01/01/70 00:00      
                        $1 in parts is not equal to $1 cost            01/01/70 00:00      
                        Oh yes, I AM still designing.            01/01/70 00:00      
                           stop whining            01/01/70 00:00      
                              it's just an illustration...            01/01/70 00:00      
                                 where does market size come in            01/01/70 00:00      
         that was said FITER not the FILTER            01/01/70 00:00      
            Sorry was a mistake it sohld be FILTER            01/01/70 00:00      
      Filter?            01/01/70 00:00      
   The illusion            01/01/70 00:00      

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