Thread: Line biasing
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Old October 26th, 2006   #2
sblair
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Andy,

Sorry for the delay...but as you guessed I was at LDI!

The Line Biasing is just to maintain the marking state. There shouldn't be any other logic or decisions based around message handling placed around it.

The "shall be enabled prior to RDM communication beginning" is a fancy way of saying it should be enabled on power up. There are some implementations where for one reason or another the line biasing my be switchable or may not be active at the instant of powerup. The main issue is that it is enabled before you start turning transceivers around and doing RDM communication, so that is why we worded it that way.

If a device receives a valid packet, it should act on it regardless of what is going on with line bias. It was never our intention that any logic be placed around sensing line bias states..

For distribution equipment I would say it is always a good idea to have the line bias in place regardless of what is going on elsewhere in the network. If you are doing RDM communication then you should have line bias regardless of what others are doing.

Also keep in mind that there is a lot of existing products out there that will be adding RDM support, but may not fully have the proper line biasing network. Odds are decent that in most cases everything will still function, so you don't want to have gear disabling communication only because it didn't properly detect a line biasing.

Nothing wrong with reporting a Status Message Warning in RDM that proper line biasing wasn't detected though.

As far as the case with legacy DMX splitters, even with proper line biasing, you may have some non-RDM devices on the same link as RDM devices, so you couldn't make decisions about line bias detection there.

Scott
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