I am an expert at digital design, but a novice at video. I have a new custom board with TMS320DM6467T (TI DaVinci SoC) running Linux with an ADV7171 DAC A output for NTSC composite video output. The ADV7171 is driving a THS7314 video amplifier. Yes, perhaps I should not have included that amplifier, but I di
I have several issues. Your help with them is greatly appreciated.
When I set MR17 for color bars, my output from DAC A looks like a rolling group of voltage levels. See the attached video. I would expect a fixed group, like figure 86. Correspondingly, my video monitor shows a bunch of gray bars with rolling brightness. So there doesn't seem to be any color information in the bars, either. (I deduce that since the height of high-freq oscillation on each bar is the same, their color is the same, and this color must be gray, or no color.)
Note I am clocking and sending data to the ADV7171 during this time. I wouldn't think the coming of data would cause this rolling...
VIDEO AMPLIFIER and SIGNAL LEVEL:
Rushed by the boss to get the board into fab, I've included a THS7314 video amplifier per a reference design based on the ADV7343. I now find that, while the ADV7343 anticipates the possibility of a downstream amp, the ADV7171 does not. Will I be successful at modifying Rset to reduce the output level, or am I best off cutting and jumpering the board to by-pass the amplifier?
Note that the ADV7171 currently has a 301ohm1% load to ground as it feeds the THS7314. The THS7314 has a couple parallel caps in series with a 75ohm1% output resistor. If need be, I can lift each chips output leg from the board, then jumper the ADV7171 output pin from the air over to the THS7314's pad to get to the output.
I would rather just adjust Rset, however, if that will get me there. I'm not worried about the highest fidelity right now. I just need to have something operational by a deadline closing in on me. I already changed Rset from 150 ohm to 1.2K (that I had in 0402 SMT sample kit, would have preferred 1K).
A gentleman on the phone at Analog Devices support mentioned "scripts" for configuring video chips. Might there be one for my application? The internal server was down when he looked. My current configuration is edited from what came inside the driver that came with my Linux operating system, git Linux-2.6.32-rc2-davinci1. Here's what I have right now. I've only changed (A) MR1, to turn on color bars and disable other DACs, and (B) turned off genlock because I have SCRESET/RTC wired to ground. (Note the driver later turns genlock on. It also sets then removes TR0RST. "HgF" notes are ones I added to the source.)
017-029.jpg is several still shots of the color bar waveform rolling around. There's perhaps 1 to to 1.5 seconds between shots. It generally takes about 5 seconds for any particular bar to roll from minimum to maximum to minimum again. This is pin 32 of the ADV7171, DAC_A.
030s.jpg is a single shot of the amplified output coming from THS7314 pin 8. This is an example of what actually goes to the monitor. "I don't know, but I've been told..." er, I mean, I think the absolute voltage levels are all out of whack, but I address signal levels in a section above.
038s.jpg is a single shot of the monitor. All the bars are gray. Their individual brightness rolls along with the waveform.
Your assistance is greatly appreciated.
[EDIT: Got color bars working via correcting inherited config per datasheet table 17, but still have questions about amp and signal level.]