Path: utzoo!attcan!uunet!lll-winken!ncis.llnl.gov!helios.ee.lbl.gov!pasteur!ucbvax!ucsfcgl!pixar!gbuce
From: gbuce@pixar.UUCP (George Buce)
Newsgroups: comp.sys.amiga.tech
Subject: LUCAS board
Summary: Improve LUCAS board stability?
Keywords: LUCAS 68020 accelerator flakey
Message-ID: <3039@pixar.UUCP>
Date: 21 Jan 89 02:40:47 GMT
Reply-To: gbuce@pixar.UUCP (George Buce)
Distribution: na
Organization: Pixar -- Marin County, California
Lines: 39

[eat me]

     Probably a rehash of older LUCAS board conversations, but I just got on
the net about a month ago and have only seen mention of the proposed memory
board design...

     I'm putting together a LUCAS board for a friend (mine will soon follow)
and I'm having difficulty with external memory.  I'm using a 12 Meg '020 and a
16 Meg '881, replaced all the PALs with D series PALs.  All other parts are the
74F series parts called for (except U9, of course).

     With the B series PALs, the only U9 I could get to work was a 74HC74
(well, it's not TTL compatible, but it works).  With the D series PALs, I can
get two 'HC parts to run and one each of 'LS and 'ALS.  I'm clocking the system
at 12 MHz (hopefully to be at 16 MHz or 20 MHz).  The system will work fine
with no external memory attached, but with a Micron 2 Meg expansion board (and
two slot box) or an Alphanetics 2 Meg board, the system hangs.  

     Did I miss any news on the net about a fix for the board that was a lot
more tolerant of changes in the system and/or didn't need the 'tuning'?  I've
got to think that with a little rewiring or a PAL change, the board would be a
lot more solid.  I'm going to put the board on a logic analyzer soon to try to
fathom the problem, but I'm hoping that someone out there has already solved
the problem and I just missed the posting.

     One tip for those about to assemble the LUCAS board:  The ribbon cable to
the disk drive is a real mechanical problem, with the folding of the cable
pressing up against the bottom of the LUCAS board.  I found that by seperating
the ribbon into 14 pairs (every other wire is a GND wire, so each pair has a
ground), the cable folds much more cooperatively.  A little care and an Xacto
knife makes splittling the cable a straightforward task.  I actually made a new,
shorter cable.  The parts are rather cheap, about $7 total.

Thanks...
_______________________________________________________________________________
George Buce                          ||  Not representing my company, but boy!
                  (8{>               ||  do they make neat toys!  (Can anyone
ubcvax!pixar!gbuce                   ||  say 48 bit planes?) (How about $30K?)
_______________________________________________________________________________