Xref: utzoo comp.misc:2231 comp.periphs:862
Path: utzoo!mnetor!uunet!ndsuvax!ncreed
From: ncreed@ndsuvax.UUCP (Walter Reed)
Newsgroups: comp.misc,comp.periphs
Subject: Re: MFM encoding question
Message-ID: <768@ndsuvax.UUCP>
Date: 4 Apr 88 18:34:58 GMT
References: <752@ndsuvax.UUCP> <1140@ssc.UUCP>
Reply-To: ncreed@ndsuvax.UUCP (Walter Reed)
Organization: North Dakota State University  Fargo, ND
Lines: 51
Keywords: MFM
Summary: Still need the info

In article <1140@ssc.UUCP> markz@ssc.UUCP (Mark Zenier) writes:
>In article <752@ndsuvax.UUCP>, ncreed@ndsuvax.UUCP (Walter Reed) writes:
>> I need information about how MFM data is encoded.  My computer writes
>> directly to the disk (It's an amiga by the way) and MFM encoding has
>> to be done.  Why do I need this info?  I am writing a conversion program
>> for IBM format to amiga and back.
>>
>
>I assume you are talking about a floppy disk, in which case you need
>the Intel or Nec databook with the 765 floppy disk chip in it.
>(Actually the Western Digital 279x datasheets have more info.)
The data sheets I've seen don't tell you how MFM is encoded.
They only tell you how big the gaps are, what sizes of sectors it can
write, how to access the chip, ...
>Unless the Amiga has a nonstandard disk controller, you only need to
It does...
>worry about the format. The number of sectors, tracks ,sector size.
>You shouldn't care about the the encoding since the NEC/Intel controllers
>and the western digital floppy controllers write the same sort of stuff.
Yeah, well unfortunately, I do need to know about the encoding.  I can
get disk format from Peter Nortons Guide to the PC, but he doesn't go into
quite enough detail.
>It only matters if you are trying to deal with something wierd like
>Apple or Commodore 64 disks.  In that case your need one of the bit
>oriented controllers like the ones Central Data or the people that
>make uniform sell for the PC.
Yep, the amiga already does this standard.  It can write GCR format too, but
I don't need that.  The amiga routines read and write an entire track at a 
time, with no gaps between the sectors except between sectors 1 & 11.  This
allows it to get 880 K on a disk instead of 720.  I can read and write a 
full track of BITS at a time, so I would set up a tracks worth of data in ram
and just write the whole thing all at once.  I guess I should have made
my previous posting more concise.  The amiga routines let you either deal
with sectors, or bits.  The amiga normally uses it's graphics coprocessor
to encode and decode MFM, but I don't have access to those routines.

Someone really needs to write a book on this subject, and if they have, I
sure can't find it.  Hell, just a magazine article would help.  (I already
checked for literiture locally available.  The Net is my last hope!)

I've gotten several replies just like the one above that basically say that
the controller does it for you.  That's true for most machines out there,
but not the amiga.  So, I still need this info!  Help! :-)

BTW, thanks to the people that already replied.

-- 
Walter Reed          PH: 701-235-0774
UUCP: uunet!ndsuvax!ncreed      BITNET: ncreed@ndsuvax or NU105451@NDSUVM1
Internet : ncreed%NDSUVAX.BITNET@CUNYVM.CUNY.EDU 
"There's no point in being grown up if you can't be childish sometimes!" Dr. Who