Path: utzoo!utgpu!attcan!uunet!ncrlnk!ncrcae!hubcap!gatech!rutgers!bellcore!texbell!killer!aimania
From: aimania@killer.DALLAS.TX.US (Walter Rothe)
Newsgroups: comp.sys.amiga
Subject: Lucas board
Keywords: Lucas 68020 68881
Message-ID: <6053@killer.DALLAS.TX.US>
Date: 10 Nov 88 06:46:01 GMT
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 37


The Lucas board is a fantastic idea that should prolong the life of the 1000
and 2000. Now if someone would just build a board like this with 64k of
32 bit direct mapped cache on board and with capability of plugging in a
68030 when it comes down in price.

There are a couple of things that bother me about the Lucas board. The first
is that the documentation says that you might have to select parts for U9.
Any design that is requires this is a commercial no-no. I question the
stability over temperature of a design like this.

The second is that there seems to be an incompatability between the 68020
and the 68000 when operated in byte mode. The 68k puts out UDS when the
byte in bits 8-15 gets put out and LDS when the byte in bits 0-7 gets
put out. The 68k manual says that that it puts the data out in both bytes
when only one of the strobes is true. However, the 68020 always puts bytes
out in bits 24-31. The problem with the Lucas board is that if you do a
byte move to an odd address, the 68020 winds up writing to bits 8-15 where
the 68k writes to bits 0-7. Am I overlooking something? I didn't see
anywhere in the 68020 manual where is says that it duplicates data on the
bus when in byte mode.

As someone else mentioned, the schematics with the distribution were in
Draw Plus format. I don't have this so I drew up a schematic on one
8 by 11 sheet of paper from the node list. If anyone would like a copy,
please send me a self addressed stamped envelope and I will send them one.
Maybe someone could convert Draw Plus to IFF and send it over the net.
One thing I didn't understand about the node list was that one address line
and one data line go to the crystal. Any help?

Walter Rothe
2008 Mary Street
Carrollton, Texas 75006

-- 
Walter Rothe at the UNIX(Tm) Connection, Dallas, Tx
UUCP: {rutgers}!smu.killer.aimania