ADV7123

I have a follow-on question:

I have looked at the ADV7344 video encoder. What will the composite output be if I put the same input in all inputs (RGB mode)? If you see the RGB to YUV conversion you obtain a monochrome signal. If the AD7344 applies this conversion matrix is it possible to obtain an image in grey scale?

In theory yes, apply the same signal to all 3 input will product a monochrome output.  However due to tolerances stack ups such as input impedances, part variations... you may get some imbalance in one of the color paths which may cause a slight color shift off of grey scale.  The best approach  would be to configure it for S-video and only use the Y signal.

Of course you could set it up for YPrPb output and only use the Y channel.

Set up a S-video demo and short out the chroma channel.  You will get only monochrome on the display.

Set up a YPrPb demo and short out the chroma channels.  You will get only monochrome on the display.

First, thank you for your reply.

About you solution for use the y channel, is not possible. Because in the input i have RGB color digital video (24bits), and in other cases i have monochrome digital video (8 bits), and i need a composite video output. In other thread i have seen  that is possible disable chroma (register 0x84 in ADV7344). And i have 2 options.

First of them, I connect 24 bits, and send information for all 24 bits in color signal case (chroma enable) and have  CVBS color output. And in monochrome case, i send information only for one of the RGB channels (G for example), and disable chroma. Do I obtain a monochrome output?

Other option is send monochrome information for each of the RGB inputs and with chroma disable kill desviation from grey scale.

I expect that someone could clarify if these is a possible solution.

S-Video is CVBS (or composite) except that the color information is on the C channel and the brightness and timing is on the Y channel.  Therefore no matter what the input is if I can get S-Video out and if I only use the Y channel then all I get is monochrome.

Using the ADV7343 as a reference (same functionality as 7344 except 8-bit vs 10-bit)

From Table 64, assuming external syncs

625i 24-bit RGB in => Y-C out, Table 81,82

625i 16-bit YCrCb => Y-C out, Table 79,80; CrCb = 128

Table 36 sets the input configuration

Table 37 sets output DAC configuration

     1) For 625i RGB, Input Mode = 000, output as Table 81 or 82 and only connect to the Y DAC per Table 37

     2) For 625i monochrome, Input Mode = 000, set C input = 128, or tie to ground, doesn't matter, set output as Table 79 or 80, and only connect to the Y DAC per Table 37

For an 8 bits monochrome input I'd set up the chip for 16 bit input with the 8 bits tied to the Y input channel and the C channel tied to ground or 128 as the setup number 2) above.

For 8-bit source, you can set Input Mode = 000 and input the 8 bits on the Y channel (same as G channel).  If you intend to use CVBS out then the C channel must equal 128.  No color is when Cr = Cb = 128.

Yes you can set it up for CVBS and kill the color via register 0x84.  There are multiple paths to what you need.  Regardless for a monochrome output you either need to kill the color burst or only use a monochrome output.