Re: 6702 chip

From: Segher Boessenkool <>
Date: Fri, 11 May 2012 19:48:27 +0200
Message-Id: <>

On Fri 11 May 2012 at 09:58:58 +0200, Rhialto wrote:
> For the moment I have pasted my lists into pastebin:

Thanks, those clarified things :-)

[skipping some 80 lines or so...  spoilers ahead...]

Still here?   Okay.

Each bit in the output is constructed independently.

[skipping some 80 lines or so...  more spoilers ahead...]

Every bit is constructed via some ring counter.  Not exactly
LFSR, but close.

[skipping some 80 lines or so...  final spoilers ahead...]

You should include the first $d6 value in the table as well,
it make it more regular.  With that done, if you look at only
at one, it stays the same for N cycles, then flips, and the
other level for N cycles.  For some of the inputs it does never
flip, stays constant all the time.  For bit K in the output,
only bit K in the input matters.  The half periods for the bits
are, highest bit to lowest: 2 5 3 1 8 7 3 6.

[okay then, final final spoilers ahead]

The circuit for each bit is a shift register with feedback, and
the value you input is also put into that feedback.  To find out
the exact feedback formulas, you'll have to put some non-constant
patterns into the chip.

This is almost a set of LFSRs by the way; except the feedback is
not linear.  But similar analysis techniques apply.


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Received on 2012-05-11 18:00:30

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