Multimaster RS485 system

[Daniel Berenguer <dberenguer@xxxxxxxxxxxx>]

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.