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From: kiki@uhunix1.uhcc.Hawaii.Edu (Jack W. Wine)
Newsgroups: comp.sys.atari.st.tech
Subject: SCSI chip project
Keywords: Help!
Message-ID: <12824@uhccux.uhcc.Hawaii.Edu>
Date: 3 May 91 08:02:06 GMT
Sender: news@uhccux.uhcc.Hawaii.Edu
Organization: University of Hawaii
Lines: 26


A lot of current discussion concerns the SCSI and a floppy chip replacement,
so this probably unoriginal thought occurred to me: replace the WD 1772 chip
with an NCR 5380 SCSI chip.  I would agree with an attempt at a floppy chip
upgrade if SCSI floppy drives were unavailable, but it seems that the logical
and physical interface space should be used for an ANSI standard SCSI port.

I managed to get an ST Internals book and it appears that the WD 1772 chip
can be replaced with an NCR 5380 SCSI chip.  The 5380 has 40 pins so an
adaptor board is necessary, but it requires almost no support chips.  I
think it needs a buffer on the data lines from the DMA chip, because TOS
will bootup and think it's configuring a WD 1772.  Also, it has three
address lines to select among its eight registers, so a free sound chip
port bit needs to be connected, but replacing the floppy chip also frees
up a couple of port bits that are used for drive and head selection.
DMA control lines have to be connected, but I don't have enough info on
either the 5380 or the ST DMA chips.

If anyone has suggestions about this possible project, please let loose
your ideas.  Also, I read that Sybex has published a new 1300 page book 
about the STE/TT computers, but their US sales office claims that it 
doesn't exist.  It may have been written by European authors, so if anyone
there can furnish me with its ISBN, I would be very happy.
 
Thanks,
Jack