[LAD] Invitation - Control Chain interface and communication protocol

[Ricardo Crudo]

hp and Karl Hammar, we already have sketch of control chain here:
http://wiki.portalmod.com/wiki/Control_Chain

On 6 November 2014 10:56, <karl at aspodata.se> wrote:

> Gianfranco (The MOD Team):
> ...
> > The physical interface of the Control Chain devices is an RS-485
> > full-duplex serial line running at 1Mbit/sec.  Currently up to eight
> > devices can be daisy chained and by use of the RJ-45 cable we also
> > power the devices ( 1 pair for input,1 for output and 1 for power
> supply).
> ...
>
> How are you handling "collisions" and idle bus (rs485 does not
> specify that kind of things) ?
>
> Idle bus can be taken care of with a resistor devider (as described
> in e.g. [1]), but that solution draws power when the bus is idle.
> Why not a "active" kind of termination by connecting "A" to +2, 3.3,
> or 5V and "B" to GND (or vice versa), both throught 60 Ohm resistors ?
>
> "Collision" handling can be avoided by using a one master and letting
> the other nodes to be slaves, and polling the slaves.
>  Or one can use something similar to J1708 [2] and CAN by driving the
> device enable pin instead of the transmit pin and let the bus "float"
> (by setting the output driver to hi-z) up/down to the "recessive" state
> by a "idle bus"/failstate circuit. You have to have some software to
> detect any collisions then.
>
> I drafted some thoughts in [3], but havn't implemented it "yet".
>
> Ideas ?
>
> Regards,
> /Karl Hammar
>
> [1] http://www.ti.com/lit/an/slyt324/slyt324.pdf
> [2] http://www.ti.com/lit/an/snla038b/snla038b.pdf
> [3] http://turkos.aspodata.se/git/openhw/serial_bus/Readme
>
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