S100 Floppy Controller Question - test-drb@ccmp.vtda.org

13 Nov 2007

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Subject: Re: S100 Floppy Controller Question
   From: M H Stein <dm561 at torfree.net>
   Date: Tue, 13 Nov 2007 01:13:48 -0500
     To: "'cctalk at classiccmp.org'" <cctalk at classiccmp.org>

---------------Original Message:

Date: Sun, 11 Nov 2007 17:51:09 -0500
From: Allison <ajp166 at bellatlantic.net>
Subject: Re: S100 Floppy Controller Question
To: cctech at classiccmp.org
Message-ID: <0JRD004G7656LL73 at vms044.mailsrvcs.net>
Content-Type: text/plain; charset=iso-8859-1

Subject: Re: S100 Floppy Controller Question
   From: M H Stein <dm561 at torfree.net>
   Date: Sun, 11 Nov 2007 17:33:20 -0500
     To: "'cctalk at classiccmp.org'" <cctalk at classiccmp.org>

<snip>
 I think Tim's point was that if your
controller's smart enough to deal with a
relatively modern 8" drive like a TM848 it could probably deal equally
well with a 5.25" HD drive and you could transparently restore an 8" image
(if you have one) to the 5.25" disk. The controller (and CP/M) would not
even know that it's a 5.25 instead of an 8"; my Cromemcos certainly don't, 
although a different FDC might well require some mods to the BIOS. 
Different FDC WILL require a different bios.  Same for SERIAL IO.

Allison

-----------Reply:

I think you might have misunderstood, Allison; sounds like you thought I was
talking about replacing an FDC with one other than what the BIOS is configured
for; obviously that will require mods to the BIOS. 
Ok, then same fdc but sufficiently differnt drive requires new (modified) bios.

Changes that affect a bios:

 Motor on/motor runs continiously.

 Step rate, head load delay, motor on delay

 Different on disk format (likely with 8 to 5")

...
 What I was responding to was a previous post that
suggested replacing an 8"
drive with a 5 1/4" HD drive might require mods to the BIOS, and I just wanted
to mention that this is not the case with a Cromemco 16/64FDC, to which a
TM848 and a JU475 appear identical as long as the jumpers on the 5 1/4 drive
are set correctly and it supplies /READY, and that this may also apply to some
other controllers. Also, if the controller has both 8" and 5 1/4 connectors and 
they are effectively in parallel as they are on the Cromemco, you may not 
even need a 50<>34 pin adapter cable. 
if the drive supplies ready _MAYBE_.  If the Drive has the same step rate.

...
 Nevertheless, controllers meant for some of the older,
non-'standard' 8" drives
probably will require changes to the BIOS, and likely also hardware mods. 
BTDT, drive changes ultimately a BIOS and in few cases the mods are small
and most not interchangeable.

Allison

...

mike 