Re: Multimaster RS485 system

[Kevin Hawkins <yahoogroupskh@xxxxxxxxxxxxxx>]

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.
>
>