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???
01/22/07 13:36
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 		 #131213 - software is not good
Responding to: ???'s previous message
I don't want software to control when PSEN is detected and when the clock stops. why? because it is generally too slow. It is just like making a CD on a 286!

I do not want to skip any bytes when writing to the EEPROM.

In my case, when the EEPROM in the system is being programmed, the WR pin on the rom is tied to an output pin (to be determined) and controlled directly by software.

I figured out last night how to make the clock stop when PSEN is low and have it start again when a signal is received from the parallel port.

I discovered the operation of the 74hc373 latch alone last night and I didn't realize that it acts as a 1-byte RAM, where the E pin (#11) changes the byte to whatever value is set.
I didn't realize that the data is retained no matter what OE is set to (pin #1). I thought that as soon as OE is high, the output is high impedance AND data is lost.

It's quite interesting the things a simple chip can offer.
I pretty much got the circuit down, now I need to make it a PCB.

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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