View Single Post
Old April 14th, 2008   #5
Junior Member
jdurand's Avatar
Join Date: Jun 2006
Location: Los Gatos, California
Posts: 3
Send a message via ICQ to jdurand Send a message via AIM to jdurand Send a message via Yahoo to jdurand Send a message via Skype™ to jdurand

Originally Posted by prwatE120
Stick to the termination details as outlined in the final, released versions of the DMX512-A and RDM standards. RDM requires the use of the line bias termination at the "controller" end of the wire, and the standard details this with topology and values.

Peter Willis
I have been carefully reading the RDM spec. and the DMX512-A spec. and they both say the termination is 120 ohm impedance, NOT resistance. Also, the RDM spec. says the differential voltage shall be at least the number specified. So, none of that precludes using the AC coupled termination which makes it easier to pass the over voltage tests, especially on a receiver. However, I see from other postings that people are trying to detect far end (DMX512-A) terminations by looking at the DC bias levels. Sorry, that won't work with AC coupled terminations.

As with many other things, it looks like if I put in AC coupled termination it will meet the spec. 100% but break other people's equipment which somehow makes it my fault (just like my 800 frame per second DMX data with low time slot counts). So, you guys win, I add large power resistors to pass the tests and keep your stuff working.
jdurand is offline   Reply With Quote