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???
07/24/05 10:18
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#97895 - More info needed
Responding to: ???'s previous message
You need to tell us more.

Are you hooking the 8255 (where did you get it, perhaps it's actually 8255A?) to the 8052 as a peripheral with R/W signals? What is your address latch?

If you are using an 8255A hooked to a real 22 MHz 8052 with a 74ALS373 address latch, then it simply won't work. It can't be fixed in software unless you have a variant that can specify wait states. (But you wrote 8052).

It gets even worse with 8052 variants which run on fewer than 12 crystal clocks per cycle. Is the 8052 a real 12-cycle part; or is it a six-, three-, two-, or 1- cycle variant?

If you have a fast 8052 and still must interface to a slow peripheral, then you might find that the simplest way is to draw vertical lines on the 8255A data sheet R/W timing and set all of the signals, in order, to satisfy the waveforms.

If someone gave you some 8255's as a gift, thank him and frame them in your personal museum.

If this is a homework assignment, you may wish to diplomatically request the instructor to explain the purpose in using this 25 year old part which is not used in industry any more. (Beware, the instructor may assign you to select a better example. :-) )

List of 39 messages in thread
TopicAuthorDate
8255 interfacing problem            01/01/70 00:00      
   well..            01/01/70 00:00      
      8255 interface problem            01/01/70 00:00      
         If you must use 8255            01/01/70 00:00      
            My datasheet says.....            01/01/70 00:00      
   Settle Erik!            01/01/70 00:00      
      8255 problem            01/01/70 00:00      
         hardware            01/01/70 00:00      
            adding to Steve..            01/01/70 00:00      
            Comment            01/01/70 00:00      
               Relic            01/01/70 00:00      
                  that was not 8255            01/01/70 00:00      
                     Actually....            01/01/70 00:00      
                        ot: 825x in PC            01/01/70 00:00      
                           Parallel port            01/01/70 00:00      
                              NOoooooooooooooooooooo            01/01/70 00:00      
                                 Ooops            01/01/70 00:00      
                                    OK I give it up! :-)            01/01/70 00:00      
                                       Just like            01/01/70 00:00      
                                 8255 in original PC            01/01/70 00:00      
               If I did not keep up with the times and            01/01/70 00:00      
                  Do your kids drive Segway?            01/01/70 00:00      
                     the real problem is not that the 82xx is            01/01/70 00:00      
                        Erik - A history lesson            01/01/70 00:00      
                           ok, even further back            01/01/70 00:00      
                              Picky, picky            01/01/70 00:00      
                                 are we getting there now?            01/01/70 00:00      
                                    Oh altight then :-)            01/01/70 00:00      
         More info needed            01/01/70 00:00      
   Pull up resistors.            01/01/70 00:00      
      Pullups            01/01/70 00:00      
   no can do            01/01/70 00:00      
      Yes he can!            01/01/70 00:00      
         does not make it current            01/01/70 00:00      
            my opinion...            01/01/70 00:00      
               did you not read            01/01/70 00:00      
                  Nope            01/01/70 00:00      
   8255 PROBLEM            01/01/70 00:00      
      10 Points            01/01/70 00:00      

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