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'SPAM: RE: [PIC] Simple PIC-to-PIC communications '
2005\05\25@132128 by PicDude

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On Wednesday 25 May 2005 12:05 pm, Jan-Erik Soderholm scribbled:
> Probably becuse RS485 isn't a *protocol*, but a specification
> of an electrical transmission medium/cabling. You don't write
> *specific* software for RS485 (like you can do for e.g. CAN).
> You have to add whatever protocol you need on top of RS485.


Good point.  I was hoping though to find an example for a 1-master, many-slave
system that could show how others have addressed some questions I have.  For
example, when the the master polls each slave, if that slave has nothing to
request, should I have it send back a response to the master saying that?  Or
do nothing and have the master wait for a timeout?  At this point, I've
decided that I would have it send back a message saying that there's nothing
to be done, but was curious how others addressed this issue.

Cheers,
-Neil.


2005\05\25@134243 by olin_piclist

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PicDude wrote:
> Good point.  I was hoping though to find an example for a 1-master,
> many-slave system that could show how others have addressed some
> questions I have.  For example, when the the master polls each slave,
> if that slave has nothing to request, should I have it send back a
> response to the master saying that?  Or do nothing and have the master
> wait for a timeout?

Yup, these are serious issues to consider.  Note that most of this is
handled by the hardware when using CAN.


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2005\05\25@134441 by Jan-Erik Soderholm

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PicDude wrote :

> For example, when the the master polls each slave, if
> that slave has nothing to request, should I have it
> send back a response to the master saying that?  Or
> do nothing and have the master wait for a timeout?

That is part of your own protocol. Do as you wish.

> At this point, I've decided that I would have it send back
> a message saying that there's nothing
> to be done, but was curious how others addressed this issue.

I made a quick google, and found this :
http://www.hw.cz/english/docs/rs485/rs485.html
Maybe you've seen it before...

Reagrds,
Jan-Erik.



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