16 Apr
2000
16 Apr
'00
6:19 p.m.
Those "special" drives are not what I meant to ask about. I want to know
more about the 8-bit mode described in the ATA Interface Specification as
published in 1994 and 1996. This is apparently a "standard" feature.
It appears that there's a control bit in one of the control registers that
allows the interface, which defaults to 16-bit mode, to be configured for
8-bit data width.
Dick
----- Original Message -----
From: Tony Duell <ard(a)p850ug1.demon.co.uk>
To: <classiccmp(a)classiccmp.org>
Sent: Sunday, April 16, 2000 12:05 PM
Subject: Re: 8-bit IDE
> Recently, as part of my effort on an S-100
"hard-card" using a 2-1/2 =
> inch ide drive, I've been revisiting the 1994 standard for the ATA =
> interface. There's a not-too-detailed mention of an 8-bit mode which is
=
set up using a
bit in register. This feature was apparently obsoleted =
as of 1996's standard. =20
I remember _special_ 8 bit IDE drives. The model numbers usually had an
'X' (for XT, I guess) in them, and they were used with special 8-bit
controller cards in PC/XT systems. I have no idea how compatible the rest
of the interface was with the PC/AT IDE drives. These drives are almost
impossible to find now, at least in any quantity.
It's actually not that hard to use a normal 16 bit IDE drive in an 8 bit
system (like an S100 card). You need a few buffers/latches to convert
between 8 and 16 bits on read/write, that's about it.
Actually, although it pains me to say this, IDE drives are so cheap per
megabyte now that you could probably get away with wasting every other
byte... Just use a 3-state buffer to always write the top 8 data lines as
0 (or FF or...) and ignore them on read. After all, people give away 1Gb
IDE drives these days (or so I've heard), and 500M of storage (i.e.
wasting every other byte) is massive for S100 systems.
-tony