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???
07/11/07 09:19
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 		 #141725 - Strictly speaking...
Responding to: ???'s previous message
Nimish Dave said:
When we erase a chips flash it is written with 1`s.

To be pedantic, erasing does not write anything - the erased state of a flash cell just reads as a '1'.

The only thing that you can actually write to flash is zeros - hence programming really just consists of setting all the required bits to '0', and leaving the others at their erased state, so that they'll read as '1's.

when "Program Counter" comes across a blank byte location it might take as instruction FF which is MOV R7,A.

Yes it will - no "might" about it.

This can actually be a useful trick to allow "patching" of your PROM: As noted above, programming is just a matter of setting erased cells to '0'; so you put a few MOV R7,A instructions (ie, 0xFF bytes - all bits in the erased state) at strategic points, and you can subsequently "patch" these bits to zeros, eg to jump to some extra code in a previously unused area of the PROM...




List of 53 messages in thread
TopicAuthorDate
Data or Instruction            01/01/70 00:00      
   Context            01/01/70 00:00      
   It does not and it cannot.            01/01/70 00:00      
      Solution            01/01/70 00:00      
         disassembler            01/01/70 00:00      
         have fun            01/01/70 00:00      
            Erase error            01/01/70 00:00      
               yes            01/01/70 00:00      
                  Certain Error            01/01/70 00:00      
                     Why?            01/01/70 00:00      
                     why?            01/01/70 00:00      
                        Why!            01/01/70 00:00      
                        Because            01/01/70 00:00      
                           what I meant by garbage...            01/01/70 00:00      
                           A single byte isn't garbage.            01/01/70 00:00      
                           D52 is open-source, isn\'t it?            01/01/70 00:00      
                              Concept of Pocket Programmer            01/01/70 00:00      
                                 well, if not            01/01/70 00:00      
                                 hummmmm....            01/01/70 00:00      
               Strictly speaking...            01/01/70 00:00      
                  @Erik            01/01/70 00:00      
                     that, in my opinion, is crazy            01/01/70 00:00      
                        It is crazy            01/01/70 00:00      
                           Eh??            01/01/70 00:00      
                              Computer here is PC (personal computer)            01/01/70 00:00      
                                 So what is the microcontroller?            01/01/70 00:00      
                        this depends on definition of "computer"...            01/01/70 00:00      
                        Here we go again ...            01/01/70 00:00      
                           beginner\'s guide to D52            01/01/70 00:00      
                           There you go again!            01/01/70 00:00      
                              Andy            01/01/70 00:00      
                                 There's always tomorrow...            01/01/70 00:00      
                                    Different application            01/01/70 00:00      
                                       Code re-use            01/01/70 00:00      
                                          the no-tool approach            01/01/70 00:00      
                                             Cell phone ?            01/01/70 00:00      
                                                PDA cellphone            01/01/70 00:00      
                                                I don't think that would be necessary...            01/01/70 00:00      
                                          Near to Cell phone            01/01/70 00:00      
                                       There are multiple ways in which to use the code            01/01/70 00:00      
                                       Still primitive            01/01/70 00:00      
                                          Good for you!            01/01/70 00:00      
                                             for displaying just 2 lines of 16 characters...            01/01/70 00:00      
                              What I mean is ...            01/01/70 00:00      
                                 Nobody did that?            01/01/70 00:00      
                                    Where you sit determines what you see            01/01/70 00:00      
                           more appropriate solutions?            01/01/70 00:00      
                              sometimes it's necessary to point out the obvious            01/01/70 00:00      
                              Another one:            01/01/70 00:00      
   It worked            01/01/70 00:00      
      Oooooh....            01/01/70 00:00      
         Sure            01/01/70 00:00      
            have a look at this!            01/01/70 00:00      

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