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RDM Physical Layer/Hardware Discussion Discussion and questions relating to the physical or hardware layer of RDM.

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Old October 31st, 2013   #1
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Default DMX splitter with Rdm - design


I am looking at designing a new DMX splitter. The question is whether I can make it RDM compliant or not, given the cost retraints.

Can one have such a splitter without a whole Proxy processor setup?

The only real porblem I see with a real basic solution is switching between tx/rx for each port.

Has anyone done something like this or have any ideas?

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Old October 31st, 2013   #2
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Originally Posted by berntd View Post
Can one have such a splitter without a whole Proxy processor setup?

There are lots of splitters out there that don't act as a proxy. I've personally build two of them, one fully manageable and protocol aware, the other extremely simple with only minimal intelligence.

The standard was specifically designed to allow for relatively simple inline devices such as splitters. Take a close look at the timing section of the standard, this is the reason you're allowed to shorten breaks for normal responses and to drop preamble bytes in the DUB response (among other accommodations).

Whichever route you go when you're designing a splitter, plan on spending a lot of quality time with your oscilloscope. Getting it "mostly right" is easy. Dealing with all the pathological corner cases is a whole lot harder.
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Old October 31st, 2013   #3
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Most of the splitters available out there that are RDM compliant do not act as Proxies. There was a lot of work done by the Task Group to make it possible to do splitter implementations that required minimal logic.

The timings are all based on giving splitters time to turn the wire around and the Discovery messages have the pre-amble that allow bytes to be dropped from it just for this reason.

At a minimum level you just need to be start code aware to know when to turn the bus around and allow return data back. It's also best if you have some jabber protection in there for a misbehaved link too.
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