Yes,  I meant it to go to the list.

John



Wireless CAN with the CANRF module.
http://www.autoartisans.com/documents/canrf_prod_announcement.pdf
Automation Artisans Inc.
Ph. 1 250 544 4950


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU] On Behalf Of Russell McMahon
> Sent: Monday, May 13, 2002 4:42 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Fw: [EE]: RF modules
>
>
> I'll pass this on to the list as that may been what John
> intended.as I had
> my "reply to" address set to me again.
> (Seems to have a mind of it's own (or of Bill's?)).
>
> RM
>
> _______________________________
>
>
> From: "John Dammeyer" <johnd@autoartisans.com>
>
> Hi,
>
> I haven't heard about Aloha since my U days.  I remember
> studying that.
> 8-)
>
> > A significant improvement is obtained by backing off for a
> > random period
> > AFTER the end of the packet being sent and then sending if
> > still free. This
>
> The alternative is what CAN does and that's arbitrate on the
> identifier
> so if a collision occurs the highest priority device gets to keep the
> channel and the others turn into receivers.
>
> <snip>
>
> > Random backoff to allow multi station competition is a
> > standard feature of
> > most collision detection schemes. Note that it should be as
> > truly random as
> > you can reasonably get to prevent some stations hogging the
> > circuit. If you
> > all drop into lockstep and compete together repeatedly you
> > can also be in
> > trouble.
>
> The biggest program can occur if all the nodes are running the same
> software using the same random initial key and for some
> reason they all
> start up at the same time. In and RF system that's not so
> likely but in
> a physical network hardwired with a common power supply that
> could be an
> issue.
>
> One thing I've done that appears to work fairly well is to use one of
> the PIC A/D channels that measures battery voltage.  Since no
> battery is
> exactly the same I get a sort of random number there.
>
> Cheers,
>
> John Dammeyer
>
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