From: ab588@yfn.ysu.edu (joseph sabatino)
Subject: Re: Percom interface
Organization: Youngstown State University/Youngstown Free-Net
Date: Wed, 26 Aug 1992 03:26:58 GMT


I got this email from Peter Haller who constructed 2 floppy interfaces
for the 8bit, one using the paralell buss
All you guys who are interested in using 720k 3 1/2" drives on your
8bits read this.
 
 
>Subject: Re: Percom Delima
>To: ab588@yfn.ysu.edu (Joseph Sabatino)
>>Reply-To: aa596@cleveland.freenet.edu (Peter Haller)
 
 
 
 
>
>
(Joe says:)
>Peter---> I am requesting info from you as to how to get an
> 8bit w/Percom interface to read 720k IBM drives.
>This is the msg you left on the clevenet atari board:
> 
> 
>>-->From: aa596@cleveland.Freenet.Edu (Peter Haller)
>>Subject: Re: ST drive to 8-bit??
>>Date: Tue Aug 14 17:59:44 1990
>>
>>
>>Well it can be done...I,ve done it ... twice and in two different ways
>>
>>1) if you have access to a Percom disk drive or rather the controler
>>to the percom
> 
(Joe says:)
>I've already done this->can't get it to format 720k ds/dd.
>(I'm using SpartaX) It says it formats at 360K ds/dd but
>it will only read/write 170 - 180k. I think its only formating 1
>side of the disk but telling me I got 1440 sectors.  It always
>comes up with "Device not present" error when I try to copy more than 170k to the disk.
> 
(Peter says)
>>you can make a small modification to the controller board - alter the 
>>timing to put it simply - and cunstruct a ribbon cable that will
> 
(Joe says)
>got the ribbon going from the drive to the add-on drive plug and have the cardedge plug hanging loose.
> 
(Peter says)
>>convert the cardedge connector to the female 34 pin connector on the
>> 3 1/2 " mechanism. I didnot use an ST drive, but with rare eceptions,
>>these drives are industry standard.
> 
(Joe says)
>I used ibm 1.44 meg floppy
> 
(Peter says)
>>2) Design and build an interface for the Parallel Expansion Bus on the 
>>800xl/130xe.  Have done this, but I wont go into it here.
> 
(Joe says)
>I would much like info on how to do this or I'll pay you to do this number for me.
> 
(Peter says)
>>And the way that was described by the sysop _ MARK?_  I saw that artical
>>in an Atati Explorer Mag ( I think).  From what I understand, the 
>>guy who figured it out is now selling the altered ROMS (Legally??).
>>But again, you need a $150-$200  drive and then have to canabalize it.
>>Not my idea of cost effective.
> 
(Joe says)
>PLEASE LET ME KNOW ALL YOU CAN ABOUT THIS ROM AND THE GUY WHO SELLS
>THESE. I have no way of getting this article in atari explorer mag
>although I'd like to read it.
>Any assistance you can give me will be appreciated....thankyou
>>>>>>>joe sabatino ab588@yfn.ysu.edu
> 
>
>--
>Joe Sabatino-->ab588@yfn.ysu.edu
>
>
(Peter says)
Joe:
 
My god! That was posted ages ago!  I am trying to remember everything I
did - I don't use my 8-bit anymore, well I do use it as a dumb terminal
for debugging Windows apps, but that's another story.
From your description, it sound like you are using a single sided Percom
controller. There were two flavors of Percom drives available. Single sided
and double sided. The single sided version requires a change in the EPROM
on the control board that talks to the 1771(?) FDC chip. The EPROM contains
6809 code, the Microprocessor that is used on the card. The Double
sided controler knows about the second side of the disk but requires a new
crystal and a updated controller chip (WD1772 i think). Regarless of the 
approach, neither of these solutions is trivial. (A 6809 cross assembler and
a machine to run such a beast on. I know of none for the 8-bit, and I hacked
a PD version for the PC to run on the ST.) 
 
As far as the Parallel bus version: This is even more of an undertaking. To
do this you will need to program a PROM to talk to the BUS and to at the
very least tell the 130xe/65xe that there is a device on the BUS. Then you
must design a disk controller circuit that can talk to the drive and 
provide an interface to the BUS. Then you must write a device driver for
the controller which must reside on the ROM also. This is how I interfaced to
a 1.44 mb drive on my 8-bit. While disk controllers are straight forward to
design - timeing is the biggest problem - today's technology actually makes it
easier with one or two ICs need for the whole thing (my board had 20!) - 
unless you are familar with digital circuit design, this could be quite an
undertaking. Also, you will need the specs on the Paralled bus and the 8-bit
internals - ie Mapping the Atari. A EPROM programmer is a must and the
MAC65 assembler cartridge for developing the code.
 
As far as me doing it for you... Well, and no offense intended, I get paid
in the range of $100 to $150 per hour for my consulting business and if you
could afford this you would be better off buy a new machine.
 
(STUFF DELETED)
 
The article I read - which I vageuly remember - documented the exact bytes in 
the EPROM memory that need to be changed. The bad news is that I sold all
of my Atari stuff with the 130xe. Magazines and everything. You might post
a message in the Atari Sig regarding this article, somebody must still have
a copy and could possibly help.
 
One last note: e-mail me at aa596 and not ae302, as I rarelu log into this
address. 
 
PCH
 
 
--
PCHaller                        | Hallsound Systems & Software
Co Atari Sig Sysop              | MIDI,Music,Recording, and Service
"If you do what you've always done, you'll get what you've always
 gotten."
 
-- 
Joe Sabatino-->ab588@yfn.ysu.edu