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From: jxh@cup.portal.com (Jim - Hickstein)
Newsgroups: comp.sys.ibm.pc
Subject: NEC SX I/O channel memory forced to 16-bit wide?
Message-ID: <27077@cup.portal.com>
Date: 19 Feb 90 01:50:21 GMT
Organization: The Portal System (TM)
Lines: 26

I am trying to get an IDEAssociates Supercomm card (PC-002) to work in
my NEC APC SX (80386SX, 16MHz), but my driver fails its RAM diagnostics.
Hopping into debug, I can see that only the even (low) bytes appear to
stick when written, the odd bytes reading back as FF.  This sure seems like
a problem with SBHE (System Bus High Enable) on the I/O Channel being
forced active, even though my 8-bit card (it's only got one edge connector,
even) is not requesting 16-bit transfers.  A quick look (hah!) at the NEC
so-called technical manual for the machine shows a memory configuration
register that can cause 0Axxxx, 0Bxxxx, 0Cxxxx, and 0Dxxxx to be either
under control of the AMMC, or on the I/O Channel.  It is configured
correctly.  I have tried moving the Supercomm card to different addresses
(it can be A, C, D, or E), putting it into the only physical-8-bit slot in
the machine (second connector not populated), and slowing down to 8MHz.
Nothing changes.

Is this a bug in the hardware, such that I cannot use 8-bit memory in these
places?  Has anyone else run across this?  What am I doing wrong?  Old-timer
that I am, I have managed to isolate it this far, but without a schematic,
I'm stuck.  I'm getting the scope out shortly, anyway.

Please respond by email.  Thanks very much.

Jim Hickstein
jxh@cup.portal.com
...!sun!portal!cup.portal.com!jxh
(408) 434-0822