S100 Floppy Controller Question
M H Stein
dm561 at torfree.net
Thu Nov 15 03:21:34 CST 2007
Date: Tue, 13 Nov 2007 07:48:21 -0500
From: Allison <ajp166 at bellatlantic.net>
Subject: Re: S100 Floppy Controller Question
>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>
>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.
Well, I should know better than to argue (again ;-) with you of all people, but...
Since we're talking about 'modern' 5 1/4" HD drives, Motor on and Ready
are jumper selectable on all the drives I've run across, step rates etc. are
faster than the 8" equivalent (except perhaps the PerScis), and with the
same speed and data rate the disk formats are identical, no?
In any case I'm only specifically talking about my Cromemco system and it
seems to work fine for me. It gives me 1.1 MB on a 5 1/4HD diskette instead
of 360KB and lets me deal with both 5 1/4 and 8" images conveniently in a
single 5 1/4" FH bay box, without the complication of the 24V supply, 50 pin
cable, unreliable old 8" drives etc. To initially read & convert my 8" disks I just
temporarily plugged an external drive w/PS into the unused 50 pin connector.
I haven't tried it yet, but it should also make recreating an 8" image on a PC
easier, and it puts some 5 1/4HD drives & disks to a good use, which otherwise
would end up on the shelf or in the trash since I don't use them on PCs.
After installing the drive I happened to run across some old posts in the archives
dealing with this very topic (on a Cromemco); apparently it was easy and worked
fine for some and not for others. I just wanted to add my name to the former
group in case it had relevance to someone else with a Cromemco FDC or
_perhaps_ even with a different make of controller if it's similar, and especially
mention to one of the original posters that it might not be necessary to kludge up a
50<>34 pin adapter cable (which he was reluctant to make) if the two interfaces
on his FDC are handled the same way as on the Cromemco FDC.
More information about the cctech