RGB Analog Output from DM644x

I am not aware of anyone that has VGA analog output using analog DACs built into the DM644X.  As a matter of fact, OSD hardware block which precedes analog DACs in the video display path converts all OSD and VID windows to YCbCr 422 format and merges them for video output.  There is no hardware block to convert YCbCr 422 to RGB after the data leaves OSD hardware block, hence the built-in analog DACs are limited to YCbCr data input and outputs TV formats such as NTSC or PAL.  For RGB output, you will probably need an external video part. 

Unfortunately the way the DACs are setup on the DM644x you cannot output VGA directly, they are only capible of outputting TV standard signals because to have the DACs enabled you must have the video encoder enabled. This said you could still have an external device output an analog VGA signal, something like a THS8200 could do the job nicely. Unfortunately I do not know of any drivers that currently would output VGA like this, however the application note below should be a good place to start to help you modify the drivers to do it.

http://focus.ti.com/dsp/docs/dspsupporttechdocsc.tsp?sectionId=3&tabId=409&familyId=1302&abstractName=spraan0

If the output can not be RGB, then why do the Functional Block Diagrams of all the Davinci devices include it as a valid DAC output option?  I thought that the VENC could be put into a RGB mode. The digital LCD data can clearly be (hence all the discussions of setting up RGB666 and RGB888 throughout the datasheet and app notes)  This RGB digital LCD data is not presented to the DACS??  (example block diagram on page 5 of the DM6441 RevD datasheet).  I was about to try this myself, This forum post has just saved me a lot of frustration ... thanks.

Where one would get the syncs is a different question. I didnt know if the digtal LCD hsync/vsync could be used with a buffer assuming the bus was in RGB mode. Perhaps the question is now moot.

The digital output certainly can be RGB compliant, and that does work, however the analog cannot output a compliant VGA/PC type monitor signal. I think this block diagram should probably be changed to not mention RGB, though it is technically correct, it is not practically correct. In other words there is nothing stopping you from outputting RGB data on the analog bus that I know of, however you would need a display that can handle RGB input in a TV standard timing pattern.

The key place I see this mentioned is the VMD bit in the VMOD register discussed in SPRUE37, in particular section 4.4.1.2 of this document mentions specifically that the DACS are disabled when VMD is set for non standard mode. This means that you cannot specify custom timings with the DACs enabled, which effectively prohibits anything other than TV standard timings, meaning a VGA/PC type output is not possible.

You can probably deduce this from Bernie's comments, but just to be clear, RGB digital LCD data is not present at the analog DACs; also, hsync/vsync are considered digital interface signals (not used with analog output), hence the reason only standard video timing modes are supported.