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???
01/29/07 18:05
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 		 #131651 - depends on the circumstances
Responding to: ???'s previous message
Erik Malund said:
"if you are pumping bits read from XDATA out as fast as you can, including a device such as the 8255 that require slowing down the execution of movx instructions will lower the bit rate. Let alone if you use such a device for the output of the bits

There is no such requirement if the CS of 8255 is held inactive during the fast XDATA access - and this would be a normal function of a normal address decoder, wouldn't it.

Of course it is assumed that there is a mechanism to slow down during 8255 access only. Standard processors do have WAIT input to stretch external bus cycles, I don't know if there is any '51 derivative with that.

If not, the 8255 would have to be bit-banged, which is not completely unfeasible either, considering it is slow anyway and the processor is fast enough anyway.

Clock-stopping comes also into mind, but that would be rather perverse, woudln't it... :-)

JW


List of 144 messages in thread
TopicAuthorDate
speed of microcontroller            01/01/70 00:00      
   crystal            01/01/70 00:00      
      Incorrect!            01/01/70 00:00      
         Sorry.            01/01/70 00:00      
   Impossible to say!            01/01/70 00:00      
      confusion            01/01/70 00:00      
         Jan you need to add            01/01/70 00:00      
            scroll down            01/01/70 00:00      
               the enlightenment that it "was explained there tha            01/01/70 00:00      
                  I may move it...            01/01/70 00:00      
   Other things            01/01/70 00:00      
   Anything can happen            01/01/70 00:00      
      That's why we have Datasheets!            01/01/70 00:00      
      switching times            01/01/70 00:00      
         the other way round            01/01/70 00:00      
         You've missed the point entirely!            01/01/70 00:00      
            Example            01/01/70 00:00      
         show and tell            01/01/70 00:00      
   where the datasheet belong            01/01/70 00:00      
      Overclocking            01/01/70 00:00      
         How maximum speed is set            01/01/70 00:00      
            you forgot            01/01/70 00:00      
               the overclockers...            01/01/70 00:00      
               Vdd and leakage            01/01/70 00:00      
                  Lynn, please....            01/01/70 00:00      
   and Lynn please ...            01/01/70 00:00      
      Are the average readers...            01/01/70 00:00      
         i do not know the 'average'            01/01/70 00:00      
            Job security            01/01/70 00:00      
         Off-datasheet operation            01/01/70 00:00      
         view of an insider to the insides...            01/01/70 00:00      
      careful now, Erik            01/01/70 00:00      
         apples and oranges            01/01/70 00:00      
            Yes, your example was 25 ppm ... ...            01/01/70 00:00      
               OT: It feels like home...            01/01/70 00:00      
                  Well ... this topic is totally exhausted ...            01/01/70 00:00      
                     as the song says "let me entertain you"            01/01/70 00:00      
                        That doesn't change anything.            01/01/70 00:00      
                            BULLSHIT            01/01/70 00:00      
                              so what? You\'ve got lots of bandwidth. Use it!            01/01/70 00:00      
                                 Once again            01/01/70 00:00      
                                    Richard, do you have an electric drill?            01/01/70 00:00      
                                    I read that ...            01/01/70 00:00      
                                       3 - three - wrongs            01/01/70 00:00      
                                    If you believe this, then read the datasheet again            01/01/70 00:00      
                                       clarification            01/01/70 00:00      
                                          OT: for all the 8255 lovers and haters...            01/01/70 00:00      
                                             It's not about the 8255, Jan            01/01/70 00:00      
                                                where thr .... did you get that from?            01/01/70 00:00      
                                                   Please clarify ...            01/01/70 00:00      
                                                      if that is what you want to call it, then yes.            01/01/70 00:00      
                                                         Well, that\'s a horse of a different color            01/01/70 00:00      
                                                            what about "roughconvert" do you not understand            01/01/70 00:00      
                                                               OK ... so that's 1250 bytes/ms ,,, or 12.5 Mbps ?            01/01/70 00:00      
                                                                  I have no intention            01/01/70 00:00      
                                                                     It won't benefit me ...            01/01/70 00:00      
                                                                        nope, for that I am paid            01/01/70 00:00      
                        OOOH! You're right ... I misread your post            01/01/70 00:00      
                           yes, stick an \'always\' in            01/01/70 00:00      
                              Are you distorting or just misinformed?            01/01/70 00:00      
                                 neither            01/01/70 00:00      
                                    now let me get this straight ...            01/01/70 00:00      
                                       This would be so darn easy to describe if I were n            01/01/70 00:00      
                                          More clarification, please, Erik            01/01/70 00:00      
                                             At the risk of entering a flame war...            01/01/70 00:00      
                                                Yes, I suspect it is ... but he didn't say that            01/01/70 00:00      
                                                   gave you all you need, if you want to argue \'possi            01/01/70 00:00      
                                                      You're wandering off track ...            01/01/70 00:00      
                                                         then how come you keep asking            01/01/70 00:00      
                                                            Because you, Erik, have overstated your case            01/01/70 00:00      
                                             the danger of 'it'            01/01/70 00:00      
                                                not quite ...            01/01/70 00:00      
                                                   Richard, I would never accuse you of such a            01/01/70 00:00      
                                                   Artist vs. engineer            01/01/70 00:00      
                                                      why, were it not for you, then ...            01/01/70 00:00      
                                                         How do I...            01/01/70 00:00      
                                                            Thre has been no other reason to bring this partic            01/01/70 00:00      
                                                               depends on the circumstances            01/01/70 00:00      
                                                                  Jan, consider the details, please            01/01/70 00:00      
                                                                     bit bang for lack of other term            01/01/70 00:00      
                                                                        Jan, that may be, but I don\'t think so ...            01/01/70 00:00      
                                                                           on interfacing both slow and fast on external bus            01/01/70 00:00      
                                                                              Your conclusion doesn't follow, Jan            01/01/70 00:00      
                                                                                 I did not discuss the appropriateness of any...            01/01/70 00:00      
                                                                     again ignoring increased interrupt latency            01/01/70 00:00      
                                                                        What latency is that, Erik?            01/01/70 00:00      
                                                                           I already did            01/01/70 00:00      
                                                                              Not exactly ...            01/01/70 00:00      
                                                                                 not me, necessarily            01/01/70 00:00      
                                                                                    Just how would that occur?            01/01/70 00:00      
                                                                                       finally you got it.            01/01/70 00:00      
                                                               Once again, Erik, you\'ve missed the point            01/01/70 00:00      
                                                                  once more ignoring interrupt latency            01/01/70 00:00      
                                                               double post again ... looks like the server\'s slow            01/01/70 00:00      
                                                         I'm lost long ago...            01/01/70 00:00      
                                                            Jan, it\'s not my \"red herring\"            01/01/70 00:00      
                                                               not so wide range of applications            01/01/70 00:00      
                                                                  What do you mean?            01/01/70 00:00      
                                                                     this discussion or engineering?            01/01/70 00:00      
                                                                        Oh, this annyoing beating arround the bush!            01/01/70 00:00      
                                                                           Sorry Erik!            01/01/70 00:00      
                                                                        Optimal? Well, maybe occasionally ...            01/01/70 00:00      
                                                                           not use antiques is interfering with progress???            01/01/70 00:00      
                                                                              Yes, the learner's progress            01/01/70 00:00      
                                                                                 Is that not obvious?            01/01/70 00:00      
                                                                                    nope ... not that simple            01/01/70 00:00      
                                                                                       in the post you are responding to!!!            01/01/70 00:00      
                                                                                    Erik, You have no argument ... just an opinion            01/01/70 00:00      
                                                                                       wrong once more            01/01/70 00:00      
                                                                                          Erik, YOU said it affects nothing            01/01/70 00:00      
                                                                                             this is NOT about \'me\' or \'mine\'            01/01/70 00:00      
                                                                                                there you go again ...            01/01/70 00:00      
                                                                                                   it has ABSOLUTELY nothing to do with any specific            01/01/70 00:00      
                                                                                                      We definitely disagree on this ...            01/01/70 00:00      
                                                                                                         if you can not accept this being general, then            01/01/70 00:00      
                                                                                                            It has to be personal and about YOU, Erik            01/01/70 00:00      
                                                                                                               I thought so            01/01/70 00:00      
                                                                                                                  Now you've proven my point, Erik            01/01/70 00:00      
                                                                                                                     back to technical ONLY            01/01/70 00:00      
                                                                                                                        So, what's the problem?            01/01/70 00:00      
                                                                                                                           what good would that do?            01/01/70 00:00      
                                                                                                                              Can't you support your dubious assertions?            01/01/70 00:00      
                                                                                                                                 no ';cases' please            01/01/70 00:00      
                                                                                                                                    Without specifics, there's no proof            01/01/70 00:00      
                                                                                                                                       I will not            01/01/70 00:00      
                                                                                                                                          All you've done so far, Erik, is huff and puff ...            01/01/70 00:00      
                                                                                                                                             I have given you 'details'            01/01/70 00:00      
                                                                                                                                                Maybe, but your \"details\" don\'t support your claim            01/01/70 00:00      
                                                                  Jan, there are always tradeoffs            01/01/70 00:00      
                                                                     forgetting the \"methods of yore\" and instead discu            01/01/70 00:00      
                                                               he can            01/01/70 00:00      
                                                                  There's a semantic problem ...            01/01/70 00:00      
                                                                     already answered            01/01/70 00:00      
                                                         Get over it, Erik ... I don't want your "secrets"            01/01/70 00:00      
                                                            once more ignoring interrupt latency bugs            01/01/70 00:00      
                                                               You keep referring to interrupts ...            01/01/70 00:00      
                                                                  I even made that exception            01/01/70 00:00      
                                                                     That's probably quite true            01/01/70 00:00      
   Why "non-specific/vague question" karma point??            01/01/70 00:00      
      You don't get more vague than...            01/01/70 00:00      
         Come on...            01/01/70 00:00      
            question vs answer            01/01/70 00:00      
            we still only guess            01/01/70 00:00      
               So...            01/01/70 00:00      

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