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???
01/18/07 16:55
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 		 #131039 - I don't think this IS critical...
Responding to: ???'s previous message
Richard Erlacher said:
If you want to change the oscillator source, you'll have to construct a circuit of some sort that swaps the clock sources without producing glitches or pulses shorter than the minimum (~41 ns, in this case) that the MCU will tolerate. This is not an easy trick, BTW.

I don't think such a strict requirement has to be met in this case... Remember, the clock swap happens (the SW driving the LPT might arrange it so that it will happen) during reset. I think, even if a glitch occurs, producing extra 24 proper clocks before releasing the reset should be OK.

JW

PS. An another idea: what about buying a commercial EPROM emulator, downloadable from PC? I use a couple of them regularly...


List of 77 messages in thread
TopicAuthorDate
I need some help with an 8051 design            01/01/70 00:00      
   Have you looked at new parts?            01/01/70 00:00      
      ROM, EPROM            01/01/70 00:00      
   Wheel Re-invention            01/01/70 00:00      
   Perhaps you\'d like to do some essential work first            01/01/70 00:00      
   Stopping XTAL?            01/01/70 00:00      
      If you know what you need ...            01/01/70 00:00      
      from the "outside" point of view...            01/01/70 00:00      
         that won't do it!            01/01/70 00:00      
   to Mike            01/01/70 00:00      
      I know my objective. I need help meeting it.            01/01/70 00:00      
         Anachronism!            01/01/70 00:00      
            not quite so...            01/01/70 00:00      
               Unfortunate            01/01/70 00:00      
               Don't blame poor MS ...            01/01/70 00:00      
                  advantages???            01/01/70 00:00      
                     I feel your pain, some of it.            01/01/70 00:00      
                  the blame game            01/01/70 00:00      
            so what?            01/01/70 00:00      
               But you said...            01/01/70 00:00      
               An attitude to learn.....            01/01/70 00:00      
               Before you get all "wrapped around the axle"            01/01/70 00:00      
                  USB as well            01/01/70 00:00      
               if you don't want to be "too" modern...            01/01/70 00:00      
                  Since you haven\'t mentioned requirements yet ...            01/01/70 00:00      
                     Even better            01/01/70 00:00      
               Hold the Reset            01/01/70 00:00      
               Mike I don't understand            01/01/70 00:00      
         you can get better than this...            01/01/70 00:00      
   One crystal            01/01/70 00:00      
      at least some people arre trying to help.            01/01/70 00:00      
         Not as simple as you think            01/01/70 00:00      
            ...            01/01/70 00:00      
               Not to beat on the data sheet            01/01/70 00:00      
               've got any schematics?            01/01/70 00:00      
         Why send NOP?            01/01/70 00:00      
            for programming/program downloading into RAM/EEPRO            01/01/70 00:00      
               ?synconisation            01/01/70 00:00      
               yes            01/01/70 00:00      
                  emulate xtal when programming            01/01/70 00:00      
                  no            01/01/70 00:00      
                     This guy has special requirements ...            01/01/70 00:00      
         WHY -WHY - WHY ON EARTH fiddle with            01/01/70 00:00      
   What!! No 8255? :)            01/01/70 00:00      
      No ... the O/P doesn't have his %$#@! together            01/01/70 00:00      
         If it is what he wants            01/01/70 00:00      
            I'm not so sure that will work ...            01/01/70 00:00      
               Comments            01/01/70 00:00      
                  He says he has an 80C51BH            01/01/70 00:00      
                     And More            01/01/70 00:00      
                     Wrong goal?            01/01/70 00:00      
                        That's true ... but ...            01/01/70 00:00      
   let's talk about this schematics            01/01/70 00:00      
      thats it            01/01/70 00:00      
         Less '245s?            01/01/70 00:00      
         Mike, why not make a list ...            01/01/70 00:00      
            I don't think this IS critical...            01/01/70 00:00      
               It\'s still not clear what he really requires            01/01/70 00:00      
                  the chips            01/01/70 00:00      
                     you are describing an ISP chip            01/01/70 00:00      
                     Well, there are ways ...            01/01/70 00:00      
         where does 12V come from?            01/01/70 00:00      
            Illegitimi non carborundum!            01/01/70 00:00      
               Au contraire            01/01/70 00:00      
                  Don't help someone's grandma across the street ...            01/01/70 00:00      
                  Moving right along!!!            01/01/70 00:00      
                     waitaminute ... it's an EEPROM ... but he's got it            01/01/70 00:00      
                        I think....            01/01/70 00:00      
                           the best laid plans of mice and men            01/01/70 00:00      
                              for a professional, EVERYTHING is an option            01/01/70 00:00      
                              It's HIS choice ...            01/01/70 00:00      
                                 yes and I gavce him two            01/01/70 00:00      
                                    Yes, I agree, one of the choices is a struggle            01/01/70 00:00      
                           thanks for your help guys            01/01/70 00:00      
                              I don't know if this            01/01/70 00:00      
                              be carefull , Mike            01/01/70 00:00      
                                 software is not good            01/01/70 00:00      

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