Re: Multimaster RS485 system

["Daniel Berenguer" <dberenguer@xxxxxxxxxxxx>]

Thanks Kevin for the link. Interesting project that SNAP.
Unfortunately, the collision detection system (if any) is not
explained in the document.

Daniel.

--- In xAP_developer@xxxxxxx, Kevin Hawkins
<yahoogroupskh@...> wrote:
>
> I haven't really looked in any great detail but SNAP is an interesting
> highly compact 'masterless' protocol - just not sure how it might
handle
> collisions ... (maybe a calculated TX delay based on address ?).
> http://www.hth.com/filelibrary/pdffiles/snap.pdf
> K
>
> Daniel Berenguer wrote:
> >
> > Hi all,
> >
> > Although it's out of the scope of this list, I'd like to start a
new
> > discussion regarding the interest/need of having a low-level
> > communication technology below xAP-Ethernet.
> >
> > xAP has proven to be a very good integration technology for the
open
> > community. I'm myself implementing this communication technology
in any
> > of my opnodes on the "Ethernet" side and I'll never
have enough
words to
> > express my gratitude to the people that started and maintain the
xAP
> > project so you can imagine how happy I am with your work, guys.
> >
> > However, as I understand the architecture of a complex control
system,
> > xAP should remain IMO on the top of the model whilst other
lower-level
> > technologies, more oriented to control applications, do the hard
work of
> > controlling/measuring endpoints. This model usually provides cost
> > reductions and simplifies the cable layout. Field technologies
that fit
> > into this category are: CAN, RS485, IEEE802.15.4, 1-Wire, etc. If
we
> > focus only on the non-commercial open protocols based on the
above
> > technologies we find:
> >
> > xAP-RS485
> >
> > Too big payload for RS485 and no collision-avoidance system
implemented.
> > Being a multimaster system, the risk of lossing messages is high
I
think.
> >
> > VSCP
> >
> > Very good project based on CAN, thus, the collision detection is
solved.
> > Excessive bitrate (500 Kbps) for my taste. Simple microprocessors
can't
> > be used as they need an integrated CAN controller or a SPI port.
> >
> > uLan
> >
> > RS485 multimaster protocol. It needs a master synchronizing the
bus I
> > think in order to avoid collisions.
> >
> > BAZ485
> >
> > Paul solves the collision problem using a simple strategy.I've
sent him
> > an e-mail with some questions though.
> >
> > Do you know of any other non-commercial multimaster protocols? I
have
> > some projects in mind consisting in a bunch of low-level
controllers and
> > I have first to decide the technology to be used. Why
non-commercial? I
> > just don't want to pay for a registration nor having to implement
> > complex protocols conceived from commercial interests. I want to
use
> > cheap microcontrollers with just one UART so RS485 seems to be
the
best
> > choice for me.
> >
> > Thank you very much for your comments,
> >
> > Daniel.
> >
> >
>