S100 Floppy Controller Question

[Allison]

>
>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