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???
10/16/06 22:19
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 		 #126545 - pins, lost&found
Responding to: ???'s previous message
Erik Malund said:
The issue is not can I use the 8255 with 'tricks' I have yet to see that question and, in addition, if you are going to use 'tricks' (I/O mapped I/O) why use the antique in the first place?


Now THIS is the question you should've asked first.
1. because my professor told so
2. because I have it on my devboard
3. because I have a handuful of them at no cost
4. because all of the above and I am a student
Otherwise, not in the first place. If it should be a new board, it should NOT be the FIRST CHOICE. However, reasons are to talk about it, still.

So, if somebody comes and asks, how to interface a 8255 to 8052, let us not answer him "don't do that" in the first place. Let us tell him, how, and then tell him that it's not the best thing to do and what are the alternatives.
In this order and say it all. Not only a part of it.


Erik said:
Another important issue re "pulling by hand" is that you can not do that when you have external memory (you do not have enough pins) and THAT is when you need I/O expansion).
Not quite so. Technically speaking, there are a couple of options, the easiest of them is to use the data/address bus pins for data/address and handle the chipselect/read/write "manually". Those who like complex solutions can cascade the 8255 with a memory-mapped latch, but I admit that would be sort of perverse a bit... :-)

Erik said:
Also if you do not have external memory what on earth to you need more than 32 (64) I/Os for?

I have around 30 switches and 20 lights in my house.

Jan Waclawek

List of 174 messages in thread
TopicAuthorDate
How to extend the ports of 8051?            01/01/70 00:00      
   I2C, SPI, 1-Wire, CPLD            01/01/70 00:00      
      Why "avoid 8259"?            01/01/70 00:00      
         Why "avoid 8259"?            01/01/70 00:00      
            Hi            01/01/70 00:00      
         Hi            01/01/70 00:00      
      Examples            01/01/70 00:00      
   Choose an 8051 w. sufficient IO in the 1st place!            01/01/70 00:00      
      all 8051\'s have the same amount of I/O            01/01/70 00:00      
         list please            01/01/70 00:00      
            typo ... sorry ...            01/01/70 00:00      
         OK then, "derivative"            01/01/70 00:00      
         huh?            01/01/70 00:00      
            I think he means...            01/01/70 00:00      
               you're right, and that's the point, actually            01/01/70 00:00      
                  cause and effect            01/01/70 00:00      
   Clarification please            01/01/70 00:00      
      Clarification            01/01/70 00:00      
         Hi            01/01/70 00:00      
            Specifics ?            01/01/70 00:00      
      Hi            01/01/70 00:00      
   8255            01/01/70 00:00      
      Avoid 8255!            01/01/70 00:00      
         8255 Is Available in India            01/01/70 00:00      
            I learned the 8085 and 8255 in college            01/01/70 00:00      
               more number blindness?            01/01/70 00:00      
                  Yes            01/01/70 00:00      
                     Actually, it IS possible ... but you\'re right            01/01/70 00:00      
                        why?            01/01/70 00:00      
                        who said useless?            01/01/70 00:00      
            so the blind should lead the deaf?            01/01/70 00:00      
               somebody's got to do it!            01/01/70 00:00      
         What do you mean by "cumbersome?"            01/01/70 00:00      
      which antique store do you shop at?            01/01/70 00:00      
   FAQ            01/01/70 00:00      
      now THAT would be helpful to many!            01/01/70 00:00      
         nobody said so            01/01/70 00:00      
            too slow?            01/01/70 00:00      
               if you want a FAQ ...            01/01/70 00:00      
                  Input or Output            01/01/70 00:00      
                     Well ... the Motorola parts did that ... bitwise            01/01/70 00:00      
                        Port C            01/01/70 00:00      
   Hi Everyboody!            01/01/70 00:00      
   Port I/O of 8051            01/01/70 00:00      
      Serial and parallel I/O            01/01/70 00:00      
         As many as two?!            01/01/70 00:00      
            port expansion            01/01/70 00:00      
               Oops - you've been in that museum again!            01/01/70 00:00      
                  that I know but            01/01/70 00:00      
                     sure            01/01/70 00:00      
                        i have not and I can't            01/01/70 00:00      
                           sorry...            01/01/70 00:00      
                     WSI; Waferscale; ST; PSM; PSD            01/01/70 00:00      
               wotizit?            01/01/70 00:00      
                  wired or line            01/01/70 00:00      
                     I'd not call it a "pin extension"...            01/01/70 00:00      
                        I would            01/01/70 00:00      
      Requirements            01/01/70 00:00      
      FAQ            01/01/70 00:00      
         a good start, but woefully incomplete            01/01/70 00:00      
            Triscend - now Zylogic            01/01/70 00:00      
            "woefully incomplete", eh?            01/01/70 00:00      
               response            01/01/70 00:00      
                  there are some \"gotchas\"            01/01/70 00:00      
                     I used them before they became flash parts            01/01/70 00:00      
                        So, where's the link to the ST software?            01/01/70 00:00      
                           let a WSI user find that out            01/01/70 00:00      
                              There are no more WSI users ... there's no WSI            01/01/70 00:00      
                                 WSI usres-PSD usres OK            01/01/70 00:00      
                           Richard... What P/N you looking at?            01/01/70 00:00      
                              I just skimmed over the four most prominent ones            01/01/70 00:00      
                           Is this it?            01/01/70 00:00      
                     PSD/uPSD            01/01/70 00:00      
   A couple of Articles on embedded I/O            01/01/70 00:00      
      broken libks            01/01/70 00:00      
         fixed            01/01/70 00:00      
      informative article(s) but ...            01/01/70 00:00      
         CPLDs and FPGAs            01/01/70 00:00      
            differences            01/01/70 00:00      
               that's not really the issue...            01/01/70 00:00      
            They\'re available at no cost            01/01/70 00:00      
               the invasion of ther windows "programmers"            01/01/70 00:00      
            re: CPLDs and FPGAs            01/01/70 00:00      
               Andy PLEASE            01/01/70 00:00      
            I only promote stuff            01/01/70 00:00      
         FPGA/CPLD drawbacks            01/01/70 00:00      
            please make complete statements            01/01/70 00:00      
               @Erik: please read complete:            01/01/70 00:00      
                  giving examples does not exclude            01/01/70 00:00      
            well, that's a big maybe ...            01/01/70 00:00      
               an example            01/01/70 00:00      
                  voltage is not my choice            01/01/70 00:00      
                     where is the beef?            01/01/70 00:00      
                        it depends            01/01/70 00:00      
                           costs less, too.            01/01/70 00:00      
   consider this ...            01/01/70 00:00      
      but why skin a cat that is rotted? the fur will no            01/01/70 00:00      
         You keep saying that, but WHY?            01/01/70 00:00      
            NO WAY            01/01/70 00:00      
               I'm not from Missouri, but "SHOW ME"            01/01/70 00:00      
                  you have now visited Missouri            01/01/70 00:00      
                     waitaminute Erik...            01/01/70 00:00      
                        and my argument is            01/01/70 00:00      
                           your argument is fallacious            01/01/70 00:00      
                              once more mixing I/O mapped and MMIO            01/01/70 00:00      
                              OFF TOPIC but...            01/01/70 00:00      
                                 it\'s the disparity between rural and urban areas            01/01/70 00:00      
                                    I do not, BUT            01/01/70 00:00      
                           pins, lost&found            01/01/70 00:00      
                              a rephrase, a question and a subject issue            01/01/70 00:00      
                                 technically            01/01/70 00:00      
                                    mixing once more            01/01/70 00:00      
                                 You're being either crazy or stupid, Erik            01/01/70 00:00      
                                    I think the crazy one is you, Richard            01/01/70 00:00      
                                       I'm a seasoned man ...            01/01/70 00:00      
                                          Same back at ya            01/01/70 00:00      
                                             Now we're into semantics            01/01/70 00:00      
                                                Now you are completely off the rocker. Who, more            01/01/70 00:00      
                                                   Wake up!            01/01/70 00:00      
                                                      that is a BLATANT LIE            01/01/70 00:00      
                                                         Good grief, Erik! It's not personal ...            01/01/70 00:00      
                                                            YES, YES and YES. I even had to code it in assemb            01/01/70 00:00      
                                                         you could state that explicitly....            01/01/70 00:00      
                                             I've tried to be diplomatic            01/01/70 00:00      
                                                I'll try it, too            01/01/70 00:00      
                                                   the IIC as an alternative            01/01/70 00:00      
                                                      As an alternative, but only sometimes            01/01/70 00:00      
                                                         two viewpoints            01/01/70 00:00      
                                                         SATA            01/01/70 00:00      
                                                            I\'d like to meet...            01/01/70 00:00      
                                                               My point            01/01/70 00:00      
                                                               Parallel works off-board as well            01/01/70 00:00      
                                                            very true, but it doesn\'t apply            01/01/70 00:00      
                                                         try THAT with the 8255            01/01/70 00:00      
                                                            Erik, it might surprise you to learn ...            01/01/70 00:00      
                                                               WHAT            01/01/70 00:00      
                                                                  Erik, in response to WHAT            01/01/70 00:00      
                                                               that implies serial, in which case the 8255            01/01/70 00:00      
                                                                  I said is was parallel-interfaced ...            01/01/70 00:00      
                                                                     Please find the word 'parallel', I may be going bl            01/01/70 00:00      
                                                                        You're right, I left it out ...            01/01/70 00:00      
                                                                           The title of nthe thread is "How to extend the por            01/01/70 00:00      
                                                                              Yes, it's HOW TO and not HOW NOT TO ...            01/01/70 00:00      
                                                                                 attaching an old ratteling caboose to a high speed            01/01/70 00:00      
                                                         not that slow - especially compared to the 8255            01/01/70 00:00      
                                                            Erik, look at the datasheet ...            01/01/70 00:00      
                                                               how do you propose to \"get it in\" at that speed            01/01/70 00:00      
                                                                  Yes, this needs clarification            01/01/70 00:00      
                                                                     no, you don't            01/01/70 00:00      
                                                                        Erik, Once again, you've brought too much to            01/01/70 00:00      
                                                                           nope, there are plenty of boards with (sorry, I kn            01/01/70 00:00      
                                                                              Well, show me ... it\'s proven untrue so far.            01/01/70 00:00      
                                                                                 I am really curious what you are making where a            01/01/70 00:00      
                                                                                    Been there, done that ...            01/01/70 00:00      
                                                                                       now you lose me            01/01/70 00:00      
                                                                                          I don\'t like \'em.            01/01/70 00:00      
                        Jan ... DIGIKEY's not always the cheapest            01/01/70 00:00      
                           of course, if you can sell the sh eh stuff            01/01/70 00:00      
                     the datasheet says ...            01/01/70 00:00      
                        are you mixing cement in a futile attempt to cast            01/01/70 00:00      
                           go back to school, Erik!            01/01/70 00:00      
                           go back to school, Erik!            01/01/70 00:00      
                              I say, you say            01/01/70 00:00      
                                 Erik, go back and read the whole thing            01/01/70 00:00      
                                    had Peter IlyitchTscaikowsky lived ...            01/01/70 00:00      
                                       one more... :-)            01/01/70 00:00      
                                          hve you see any post stating that?            01/01/70 00:00      
                                             yes. Richard's... :-)            01/01/70 00:00      
                                                and that was because ...            01/01/70 00:00      
   Why is this so endlessly fascinating?            01/01/70 00:00      
      to Jez            01/01/70 00:00      
         i dunno            01/01/70 00:00      
   "Extending Input/output"            01/01/70 00:00      
      "Extending Input/output"            01/01/70 00:00      

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