31 Jul
2004
31 Jul
'04
9:11 p.m.
In message <006c01c47778$a180f320$6400a8c0@HPLAPTOP>
"Jay West" <jwest(a)classiccmp.org> wrote:
It was Bob that told me he had pretty pitiful luck
with finding ones, and
the ones he did find had a very low success rate. Hence, the discussion of
EPROMS and SRAMS.
What about using a GAL programmable logic chip?
Use CUPL's "lookup table" feature, use the 8 (or was it 9?) inputs on a
GAL16V8 as address inputs and use the outputs as data outputs. IIRC the
propagation delay for a normal GAL is 15nS, but you can get them in speeds
down to 7nS.
Pricing in 10-off for GAL16V8D-QP chips was somewhere around ?1 ($2) each
last time I ordered some.
As far as programming goes, there are designs for a programmer called the
"GALBlast" floating around the 'Net. Make sure you get the latest version
(1.6 IIRC) from the author's homepage. I found a single-sided PCB layout
that used an R2R ladder on a site called "mpu51". I subbed a BFY51 for the
power switching transistor and a BC557 (jellybean PNP) for the PNP
transistor. It seems to work fine, but the 7805 NEEDS a heatsink, unless you
feel like trying to work out why the programmer won't work. I used a piece of
scrap aluminium sheet, bent into a flattened "U" shape.
The source code is included with the programming software, so you could
probably write your own driver to run it. IIRC the guy who designed the
GALBlast was Manfred Winterhoff (aka MaWin).
My GALBlast works, but YMMV.
Later.
--
Phil. | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
philpem(a)dsl.pipex.com | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.dsl.pipex.com/ | 48xCD, ARCINv6c IDE, SCSI
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