I'm not sure if I'm reading this wrong or something, but this is a trace of the DMX packet that's coming from my USB-RS485 module then being converter to UART logic levels for my microcontroller.
There are a few things I don't think are right...
What I assume is the 'break' is only the width of one frame, but by definition in the standard is is more likely to be twice this size or greater.
The 'Mark after break' is huuuuge. From the scope you can see it's about 116 us wide, when it should really only be 8
Lastly, there doesn't seem to be a 'start frame'. When set channel 1 to any value, it goes into the first frame after what I've assumed is the extra long 'Mark after break'
Am I missing something here or misinterpreting the DMX protocol? Right now I'm using Freestyler to drive the RS485 device as an ENTTEC OpenDMX transmitter. Anyone have any ideas? is it a software or set up thing? I also tested a tool called KMTronic DMX device tester, and it's given me the same sort of output.
I've just noticed after looking at the differential RS485 lines (see above picture): It looks like that low at the beginning actually is a frame (maybe the start frame?). I can see the line go from an unknown state to driving high for 4us(Mark-time-between-packets?), drive low for the frame of 44us, then drive high for 8us (typically a stop bit time). After that the line goes to an unknown state again. Really strange and confusing. If that's the case though, then I have nothing that even resembles a 'break'.
Also for those unfamiliar with DMX packet structure: http://www.dmx512-online.com/gifs/dmxpack.gif