S100 Floppy Controller Question

[Allison]

>
>Subject: Re: S100 Floppy Controller Question
>   From: M H Stein <dm561 at torfree.net>
>   Date: Thu, 15 Nov 2007 04:21:34 -0500
>     To: "'cctalk at classiccmp.org'" <cctalk at classiccmp.org>
>
>---------Original Messages:
>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>
>
><snip>
>>
>>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.
>
>-------------Reply:
>
>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?

the drive used are a factor and many of the later designed systems 
had what could be described as an adaptive, they have a bios written 
to accomodate a wider variety of drives.


>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.

Cromemco is one such example and much later than Altair/Tarbell.


>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.

Same was the case for AmproLB, SB180, and Compupro.  Generally most fo the 
floppies are close to "setup, plug and play".  However really old drives
for example SA800, SA400 it's fairly easy to get the signals right but things
like 40ms step rate (sa400) and 12ms step rate(sa800) have to be driven
by software. After about 1981/82 design had fewer problems and 5.25 floppies 
started to look more alike than different electronically.

The gotchas still lurk out there.

Allison

>mike