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Jan Waclawek
03/08/12 00:35
  03/08/12 00:37

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#186496 - fuse bits
Responding to: ???'s previous message
Jon Wilder said:
I have an AT89S8253 that I would like to erase. However, I think the firm that programmed it cleared the SerProgEn fuse on it, which would prohibit my AT89ISP cable from being able to do it. Does anyone know of any parallel programmers that will allow me to erase the chip and reset the SerProgEn fuse to allow future programming via the ISP programmer?

AT89S8253 datasheet said:
Serial Programming Fuse: A programmable fuse is available to disable Serial Programming if the user needs maximum system security. The Serial Programming Fuse can be disabled via both the Parallel/Serial Programming Modes, but can only be enabled via the Parallel mode.
The AT89S8253 is shipped with the Serial Programming Mode enabled.

I believe every parallel programmer capable of programming the AT89S8253 allows to set any of the fuses. I quickly checked my favourite Elnec programmer's software and there is nothing which would indicate otherwise.

Just a note, although not crystal clear from the datasheet, I believe that the fuses are not changed during chip erase.

Also, with care, you might be able to set up a simple rig to write the serial enable fuse to required state - all the needed information is in the datasheet.


List of 7 messages in thread
AT89S8253 SerProgEn Fuse      Jon Wilder      03/07/12 18:18      
   Situation Vague      Michael Karas      03/07/12 23:38      
   fuse bits      Jan Waclawek      03/08/12 00:35      
      I have plenty of 8253's in stock...      Jon Wilder      03/08/12 08:44      
         Unless You Call a Favor      Michael Karas      03/08/12 13:53      
            what's hobbies about      Jan Waclawek      03/08/12 22:43      
               Unlocked      Jon Wilder      03/16/12 06:05      

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