The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
From: "Tauno Voipio"
References: <3DA2D6FC.B68FEBC@yahoo.com> <3DA2EF5A.E07DAA01@webaccess.net> <3DA3057C.9C4AE87D@yahoo.com> <3DA33E44.FE8D2642@yahoo.com>
Subject: Re: Looking for MFM endec description
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Wed, 09 Oct 2002 12:21:58 GMT
NNTP-Posting-Date: Wed, 09 Oct 2002 15:21:58 EET DST
Organization: Sonera corp Internet services
"CBFalconer" wrote in message
> Grant Edwards wrote:
> > In article <3DA3057C.9C4AE87D@yahoo.com>, CBFalconer wrote:
> > >> Contemplate some fun codes now. How about an RLL code that is
> > >> also DC free?
> > >
> > > Obviously impossible on a bit by bit basis. But it should be
> > > possible to encode each of a particular N bit sequence into
> > > some M > N bit pattern that would be DC free, and table drive.
> > > How to create a DC free sync pattern? The result would be
> > > useful, especially for long line communications.
> > Manchester encoding has been used for that for a long time (N=1
> > and M=2).
> But that doesn't get the reduced bandwidth/transitions of a longer
> code. The DC doesn't usually matter for such things as local disk
> drives, but the transitions do. Both are of interest for long
> distance transmissions.
Please note that the pulse stream is not fed directly to the write head in
the disk drive. The pulses feed a divide-by-two flip-flop whose output is
fed to the write head, so each pulse creates a transition in the
magnetisation state. This signal is nearly DC-free.
When reading, the transition pulses are full-wave recitfied and
stretched/cut to standard width, so the information is in the timing of the
leading edges of the pulses.
tauno voipio @ iki fi
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup