Yes, you are correct of course. This is sort of a poor man's Manchester
because it doesn't require a PLL to recover the clock. Real Manchester
doesn't have to use level shifts -- some use phase shifts. But either
way, the shift is in the middle of the bit boundaries.

Anyway, yes -- that was pretty much incorrect and thanks for keeping me
on my toes.

Al Williams
AWC
* Easy RS-232 Prototyping
http://www.al-williams.com/awce/rs1.htm



> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Tim H.
> Sent: Friday, February 08, 2002 8:56 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [PIC]: RF Transmitters - Micro size
>
>
> Hi Al,
>
> I've been pursuing an RF link myself so any relevant info I
> find is helpful. So, I decided to check out your design. I
> skipped ahead to see what kind of encoding method you're
> using. I then came across this:
>
> "A short pulse is a 0 and a long pulse is a 1.
> This is Manchester encoding and has the benefit of being
> self-clocking and relatively immune to time variations."
>
> >From what I know, this isn't Manchester; it's pulse-coded data. It's
> what Sony uses for their IR protocol. Manchester on the other
> hand represents 1s and 0s by change of signal level. Each bit
> uses the same amount of time but it cuts your total bandwidth
> in half. To send a logic one, you hold the line low for half
> a bit period then yank it high. For a logic zero, you hold
> the line high for half a bit period and pull it low. Of
> course, this isn't carved in stone, I've seen designs reverse this.
>
> If I'm totally wrong, please forgive me.
>
> -Tim Hamel
>
> Al Williams wrote:
> >
> > Our "Basic Stamp Project of the Month" this month is relevant. The
> > system I show is slow and one way, but it is cheap (maybe
> not quite as
> > cheap as the -um- machine) and readily available. A PIC
> could drive it
> > much faster (much of the slow speed is to allow for the Stamp's
> > processing latency) although it would never be high speed.
> In theory,
> > you could adapt the system for two way, although I haven't
> personally
> > done this.
> >
> > Anyway, might spur some ideas. The project of the month
> changes each
> > month and is always at: http://www.al-williams.com/awce/som.htm
> >
> > We call it the Basic Stamp Project of the Month, but we
> occasionally
> > do PIC, SX, or just general-interest projects.
> >
> > Good Luck!
> >
> > Al Williams
> > AWC
> > * Check out our PIC Programming Tutorial
> > http://www.al-williams.com/pictutor
> >
>
> --
> http://www.piclist.com hint: The PICList is archived three
> different ways.  See http://www.piclist.com/#archives for details.
>

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