I do have jpegs of this board if anyone is interested.
--- Tony Duell <ard at p850ug1.demon.co.uk> wrote:
On Sunday 20 January 2008 21:08:51 Chris M wrote:
> 16L8ACN. This is the PAL aboard the Acculogic
> sIDE-1/16 XT-IDE controller I mentioned. Someone
asked :)
... and here's a datasheet.
http://noel.feld.cvut.cz/hw/philips/acrobat/6052.pdf
Now, correct me if I'm wrong, but that seems to
suggest that some of the pins
are always inputs, and some may be configured as
inputs or outputs.
Correct. The 16L8 (IIRC) has 10 pins that are always
inputs, 2 pins that
are always outputs amd 6 pins that can be configured
as either. And note
that you can take feedback from those 6 (if
configured as outputs) into
the logic array, thus meaning you can make
sequentioal circuits
(flip-flops, etc).
That last can really complicate things. It means,
for example, the
concept of a truth table may not be valid (it's a
'sequence table', and
that just cylcing through all the inputs and seeing
what the outputs do
is not enough. However, note there is no 'hidden
state'. If the chip is
programemd to make flip-flops, etc, then the output
of each flip-flop
appears on a pin (this is not true of more complex
programmable logic
chips). So there is some hope in cracking it.
I reckon it would be possible to work out what's
configured as input and
what's configured as output, and from that
determine the truth table of the
PAL by brute-force methods (just try all the
inputs in turn). From there you
can start looking at how to reproduce it.
I would start by tracing scheamtics of the board if
you;ve not already
done so. That should tell you which pins are inputs
and which are outputs
(and which, if any, are bidirectional). It may also
indicate if the
device is possibly sequetional (if, for example,
it's just an address
decoder, then it's very likely to be purely
combinatorial).
-tony
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