Re: 6702 chip

From: Groepaz <groepaz_at_gmx.net>
Date: Fri, 11 May 2012 06:32:20 +0200
Message-Id: <201205110632.20968.groepaz@gmx.net>
On Thursday 10 May 2012, you wrote:
> Having just coded up the VHDL for the CRC computations for both ethernet
> and HDLC then I would suspect that the internals of the 6702 are a state
> machine that depends upon the value written and the current value. The XOR
> operator and logical shifts (left or right) or rotates (left or right)
> will also come into the equation. So keep an eye out for these operators
> in the numbers that get spat out. As Segher has already hinted - convert
> the numbers to hex, octal or binary rather than decimal and you may see
> the pattern easier. If we can get a printout of the exact number sequence
> on this thread (and the values you poked in to obtain them) this would
> allow some degree of 'parallel processing' to the problem. Multiple
> hackers working in different time zones all with different ideas working
> on a single problem - either a recipe for disaster or success! Cheers,
> Dave

i'd start with feeding it a pattern that contains the minimum number of 1 bits 
which will still produce a non zero output (if it produces a non zero output 
with just zeros as input, even better). that should reveal quickly if it is 
some kind of lfsr, or something simpler.

-- 

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Freedom of the press belongs to those who own one. 
<A. J. Leibling>


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