Subject:
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Re: Brainstorms -- A Simple Unique Addressing Scheme
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 14 Aug 2002 03:26:55 GMT
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Reply-To:
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Dick Swan <dickswa@sbcglobal.netSPAMCAKE>
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Viewed:
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1033 times
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There's been a lot of messages on how to determine unique addressing
for intelligent peripherals.
Model railroading has solved this problem in a fairly easy way. THe
NMRA (National Model Railroading Association) defined the DCC (Digital
Command Control) protocol ten years ago as an industry standard to
allow smart controllers to separately address and control multiple
train locomotives on a single track. The two rails of the track carry
both DC power and the signaling messages. DCC also allows for output
control of peripheral devices likes track switches, lights, etc.
Details on the standard are at
http://www.nmra.org/standards/consist.html#standards-DCC.
Carrying both DC power and signaling on a single pair of wires (i.e.
the track) also solves another problem posed in this thread. And the
control signal is agnostic to the polarity of the power applied to the
tracks. The control channel operates in a 10 KHz to 100 KHz carrier
above the DC signal on the tracks.
Each train locomotive or other peripheral contains a smart uniquely
addressable controller. End users initially program the peripheral
address themselves. A simplified view of the procedure is to put the
locomotive on a dedicated short section of track and then send a DCC
broadcast command to the locomotive to set the new address. The
locomotive is the only device on the track (i.e. signalling bus) so
only one locomotive / peripheral is programmed to this address.
Naturally, in the case of a robot you have to assign the peripheral
addresses before you build your robot.
DCC message decoders can be really small and would fit in a 2x4 lego
brick. A message decoder with integrated motor control (forward,
reverse, brake, float, multiple PWM speeds, etc) can be as small as
0.55" x 0.38" x 0.16". See
http://www.tttrains.com/nmradcc/rp911.html#appendix_a.
Unfortunately, the DCC is a one way only protocol. Messages are sent
from the main controller to the peripherals / locomotives. I don't
think the standard allows for messages in the reverse direction.
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Message has 1 Reply:
 | | Re: Brainstorms -- A Simple Unique Addressing Scheme
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| (...) [snip DCC references] (...) That might be workable. I2C does not really have a broadcast message (General Call is close, but not quite). However, just scanning the I2C bus for 1024 addresses to find what the current address of the module is (...) (22 years ago, 14-Aug-02, to lugnet.robotics)
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Message is in Reply To:
| | Re: Brainstorms
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| (...) There are only 1024 maximum addresses. There are more than 1024 I2C chips out there. Ergo, there are address conflicts between some of the chips out there. Unfortunately, there is no requirement that 2 chips at the same address implement the (...) (22 years ago, 13-Aug-02, to lugnet.robotics)
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