[Diy_efi] Re: Reversing EPROM decryption board

[Stevan Glogovac]

I've built the data bus spy. NVRAM is DS1230Y, datasheet available at: http://pdfserv.maxim-ic.com/en/ds/DS1230AB-DS1230Y.pdf. 
   
  The results are weird, so to say. If I test it with ordinary EPROM containing my program (PEELs bypassed, so CPU reads the EPROM directly), NVRAM is getting filled correctly... just like it is supposed to do.
   
  Once I use encrypted EPROM and put the PEELs back in picture, it doesn't work. The ECU won't even boot, so it must be reading some crap of data. Not to mention that the contents of NVRAM is just proving that... 
   
  What the hack is going on? 
   
  Of course, I checked the spy board many times, it was all perfect.. and it runs with EPROM, so there should not be a problem there...
   
  Ideas?
   
  Regards,
  NG
   
  ************************************************************************************************
  You will need to play with the NVRAM's /CS. If there is a separate /RD line,
tie that high and try tying /CS low (and pull it high before shutting down to
prevent spuriuous writes). If that doesn't work, you can try tying /CS and /W
together but it would be best to poke around looking for another signal that
would correspond to the EPROM /CS, maybe one of the PEEL inputs.
It's usually better to have /WR framed by all the other signals.
If the NVRAM has one RD/WR line rather than separate /RD /WR lines,
tie RD/WR low and tie /CS to /OE.
If the NVRAM has any /OE input, tie that high to prevent bus contentions.
These are general rules-of-thumb. Let me know your NVRAM part number and
an URL for the data sheet, if you have that.

-- Don

 		
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