multi-drop networking protocol?

PatM · Joined: 25 Oct 2004 Posts: 104

I want to start playing with networked chips (RS-485 most likely) and while the hardware part is simple I'm having a hard time figuring out (or finding) a protocol to use.

For the most part this would be a master to many slaves network (easy enough) but I was thinking it would be good to have the network auto-configure when another slave is added. The obvious way would be to have a newly added slave send out a "I'm here" message so the master can add it to its routines. Of course, the immediate thought that came to mind is managing the bus. What another unit starts talking at the same time and the packets collide? Perhaps theres a way to have the master detect and interrogate the new unit?

I know many people must have had to handle this kind of thing and found solutions and I'm wondering if any has a link to something along those lines?

bzijlstra · Posted: Sat Feb 16, 2008 4:52 pm Post subject: BenBus...??

With Bascom-8051 I have done this...

http://members.home.nl/bzijlstra/software/communication/Benbus.htm

And with Bascom-AVR we have done this...

http://members.home.nl/bzijlstra/hardware/stepper/stepper.htm#boorautomaat

The communication between the three steppermotorboards and the masterboard is done with the BenBus-protocol (RS485).

Have fun
Ben Zijlstra

PatM · Joined: 25 Oct 2004 Posts: 104

Yeah, I've done similar between a master and slave. What I'm looking for is something that deals with auto-configuration.

The easy way is to assign addresses on each board (physical or software) then tell the master to talk to the new unit. I'm thinking more along the lines of putting an un-addressed unit into a network, have it annouce its presense, then have the master assign the address. If a unit is removed, the master should notice and stop trying to talk to it.

Sounds easy but without something like an attention line (pull low to tell everyone not to talk because you're doing so) you could just inject bytes into another unit's message and screw up both of them.

bzijlstra · Posted: Mon Feb 18, 2008 10:01 am Post subject: Sweep

Perhaps you can do a sweep every n minutes initiated by the Master.

Have fun
Ben Zijlstra

PatM · Joined: 25 Oct 2004 Posts: 104

I was thinking that very thing Wink

Since this is RS-485 about the most units you could possibly have would be 128 (all 1/4 UL chips). In this particular application I can't see having more than 6 but it'd be nice to have a generic protocol.

I could broadcast a "Anyone new?" packet once a minute (probably overkill but not onerous. On powerup (after power failure) the master could step through all possible addresses with a "Are you there?" packet (optinal setting on master for "highest address"?).

Hmm, have to do a lot of thinking about this.