ADV7842 with non-standard composite video

Hi,

  Please let us know whether that CRT TV supports an HDMI port

  Kindly provide the model number of your CRT TV and describe the method you are using to establish the connection.

  And enable the auto-detection mode, which will automatically detect the video format based on the input, even if the corresponding register setting was missed to enable.

Also, Please ensure with below register when using VCR as input,

Thanks,

Poornima 

The CRT only has composite inputs and supports NTSC, PAL-M, PAL-N, PAL-BG, it automatically switches between 50Hz and 60Hz according to the signal. If I connect the VCR directly to the TV using composite video I get a color non-cropped image at 50Hz. If I use an HDMI to composite converter to do VCR - Eval board - TV I get the same image (cropped or BW image) as the examples in the post, because the signal got digitized with bad parameters.

Here are the status registers while playing the tape:

PAL-M forced (image has correct colors, but the bottom is cut off)
STATUS_LETTERBOX_TOP = 0x00
STATUS_LETTERBOX_BOTTOM = 0x00
STATUS_LETTERBOX_SUBTITLES_BOTTOM = 0x00
STATUS_NOISE_LEVEL_LSBS = 0x04
STATUS_MACROVISION_DETECTION_1 = 0x00
STATUS_MACROVISION_DETECTION_2 = 0x00
STATUS_ACTIVE_STANDARD = 0x14
STATUS_NOISE_LEVEL_MSBS = 0x00
STATUS_LUMA_GAIN_1 = 0x04
STATUS_LUMA_GAIN_2 = 0x0B
SDP_STATUS_INPUT_TYPE_1 = 0x78
SDP_STATUS_INPUT_TYPE_2 = 0x08
STATUS_PR_SD_DETECTION = 0x31
STATUS_BURST_LOCKING = 0xCE
STATUS_INPUT_TYPE_3 = 0x5F

PAL forced (no color, image is correctly sized)
STATUS_LETTERBOX_TOP = 0x00
STATUS_LETTERBOX_BOTTOM = 0x00
STATUS_LETTERBOX_SUBTITLES_BOTTOM = 0x00
STATUS_NOISE_LEVEL_LSBS = 0x04
STATUS_MACROVISION_DETECTION_1 = 0x00
STATUS_MACROVISION_DETECTION_2 = 0x00
STATUS_ACTIVE_STANDARD = 0xBE
STATUS_NOISE_LEVEL_MSBS = 0x00
STATUS_LUMA_GAIN_1 = 0x04
STATUS_LUMA_GAIN_2 = 0x0B
SDP_STATUS_INPUT_TYPE_1 = 0xF0
SDP_STATUS_INPUT_TYPE_2 = 0x48
STATUS_PR_SD_DETECTION = 0x31
STATUS_BURST_LOCKING = 0x48
STATUS_INPUT_TYPE_3 = 0xDF

Auto-detection (detected as PAL-N, correct size but with wrong colors exactly like the video above)
STATUS_LETTERBOX_TOP = 0x00
STATUS_LETTERBOX_BOTTOM = 0x00
STATUS_LETTERBOX_SUBTITLES_BOTTOM = 0x00
STATUS_NOISE_LEVEL_LSBS = 0x04
STATUS_MACROVISION_DETECTION_1 = 0x00
STATUS_MACROVISION_DETECTION_2 = 0x00
STATUS_ACTIVE_STANDARD = 0xBC
STATUS_NOISE_LEVEL_MSBS = 0x00
STATUS_LUMA_GAIN_1 = 0x04
STATUS_LUMA_GAIN_2 = 0x0B
SDP_STATUS_INPUT_TYPE_1 = 0xF0
SDP_STATUS_INPUT_TYPE_2 = 0x48
STATUS_PR_SD_DETECTION = 0x31
STATUS_BURST_LOCKING = 0x4A
STATUS_INPUT_TYPE_3 = 0xDF

Hi,

  Please check whether the 'HDMI to Composite' convertor causing this issue.

 To confirm this, Kindly replace our evaluation board with other supported device and verify if the issue persists.

Thanks,

Poornima

20-inch LCD TV, via Composite

32-inch LCD TV, via Composite

CRT TV, via Composite

All the images above are connected directly to the VCR via Composite, without the eval board. Only the CRT correctly displays the image. Any device that digitizes the signal fails with this one because PAL-M at 50Hz should never occur, but this VCR outputs it. The eval board works correctly if I input a standard signal (PAL-M 60 Hz, NTSC, PAL).

What I'm asking is if there is some way to force the ADV7842 to output 625-line 50Hz signal with PAL-M color decoding. Forcing it to PAL-M correctly decodes the color but the picture is cut off because the output is always 525-line 60Hz when selecting PAL-M. I'd need some way to control the frame rate and color decoding separately.

Could you please check with an expert about this? I already read the datasheet and user guides several times from start to finish and couldn't find a way to influence the output resolution that is not tied to the color format.

Hi,

  In our ADV7842/ADV7511 evaluation board we verified PAL with 50Hz refresh rate with different sources but we don't find any issues. Here we don't have VCR source to verify the same.

  Could you please try with below referred SFL registers and let us know the result.

  Generally SFL pin was designed for VCRs and other video sources that can output horizontal lines of CVBS at non-standard length.

Thanks,

Poornima

I tested all SFL combinations and they did nothing. After testing a few more things I managed to get a bit further with these registers.

SDPIO Map

A0 05

A1 05

A2 05

A3 05

A4 05

A5 05

A6 05

A7 05

A8 05

A9 05

AA 05

AB 05

AC 05

AD 05

AE 05

AF 05

I also had to disable the frame TBC with SDP 0x12 to 0x01 and force PAL-M with SDP 0x00 to 0x04. The frame TBC converts everything to a standard 480i60 signal because it is configured as PAL-M.

This produced a 576i50 image with the complete frame visible and instead of cutting the bottom it stops decoding the color.

I'm using the ADV7842 because it has frame TBC, I really need it to be enabled for this chip to be useful with VHS. So the question now is how to fix the color decoding and make the frame TBC output as 576i50 when PAL-M is selected.

Hi,

  TBC (Time Base Correction) is a feature meant to correct timing issues for video generated with old VCR players so we should not turn off the TBC.

  I suspect that the 'HDMI to Composite' converter is causing this issue, as we do not face it on our evaluation board when using other sources and sinks (Support HDMI).

  Please change 0x00 to 0x0E since PAL-BGHID matches the actual 625i/50Hz and let us know.

Thanks,

Poornima

Let me clarify some points we discussed so far.

I'm testing a PAL tape on a PAL-M/NTSC VCR. It produces a non-standard video that has PAL size but PAL-M color. I don't think any test equipment has a mode with this output because it should not exist, but this VCR does it anyway. On a CRT TV the sync goes to one circuitry and the color goes to another, it doesn't matter if it's not standard, it will display the image correctly and the VCR makers used that property.

The HDMI to Composite converter was brought up because if I were to connect the eval board to the CRT I would need this adapter. I didn't do that at any time because it's not necessary to this troubleshooting. My tests were done with either an HDMI capture card or connected to a TV via composite or HDMI. No matter where I connect the eval board, the image is the same because the ADV7842 already messed up the analog-digital conversion. The ADV7511 part of the board is fine. All my images here were HDMI through the eval board except when stated.

The issue here is that the ADV7842 doesn't understand the mix between PAL and PAL-M (which is similar to NTSC) in the same signal. PAL-M has the same resolution and refresh rate of NTSC, 525 lines 60 Hz, but uses PAL modulation at 3.575611 MHz. PAL has a resolution of 625 lines at 50 Hz with chroma frequency of 4.433619 MHz. I confirm that a standard PAL-M signal works perfectly with the ADV7842, so does a standard PAL and NTSC signal.

To replicate this scenario with test equipment, you would get a PAL signal and shift the subcarrier frequency to 3.575611 MHz, just like a NTSC 4.43 signal. I guess the VCR manufacturers wanted to save a few cents and reused the PAL-M crystal instead of adding a PAL-N crystal at 3.582056 MHz and since CRTs don't care about the mismatch, they went with it. This 6.445 KHz difference in the subcarrier makes the ADV7842 almost lock to the signal, you can see in the first post the PAL-N capture has some color but they are not stable. If there is a way to expand the subcarrier tolerance it may work as well.

There doesn't seem to have a public register in the ADV7842 that can control the subcarrier frequency independently of the sync frequency. If I set it to PAL-BGHID it expects exactly 625/50/4.433619, if I set to PAL-M it expects exactly 525/60/3.575611. For everything to work I'd need to configure the ADV7842 to have the 3 values in bold at the same time. The only publicly available options are PAL which covers 2 of 3 parameters, or PAL-M which covers 1 of 3 parameters.

The TBC is doing its job of getting a non-standard signal and outputting a standard signal, but with the bad parameters it ends up producing a cropped image or black and white image and "baking" it into a stable HDMI signal, like I demonstrated in the first post. It is not the TBC's fault, it's the decoding before it. There must be a way to modify the input parameters outside of predetermined combinations. Someone with knowledge of the inner workings of this chip would figure this out in no time.

The SDP_STD register you mentioned is read-only, but I tried writing to it anyway and it made no difference.

Hi,

As previously mentioned, we have validated PAL at a 50Hz refresh rate on our ADV7842/ADV7511 evaluation board using multiple video sources, and no issues were observed during testing. However we do not have VCR source in our lab to replicate the exact scenario you described.

Your query has been forwarded to our part specialist team for further analysis. We will provide an update as soon as we receive their feedback. While we are currently unable to offer a specific timeline, we appreciate your patience and will keep you informed of any progress.

Thanks,
Varshini K

Hi. Is there any update from the part specialist on this?