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TVP5150AM1, are the VBLK positions BT.656 compliant

Other Parts Discussed in Thread: TVP5150AM1

I am relatively new to the Video capture world, so please excuse any 'obvious' errors.

I am playing with a TVP5150AM1 as part of a USB Video Compliant (UVC) frame-grabber solution.

The frame-grabber requires signal for LineActive and FrameActive. At the moment I am concentrating on a PAL source.

I have the TVP5150AM1 configured as:

  • Output ActiveVideo (which I am using as my LineActive signal)
  • VBLK (which I am using as FrameActive)
  • 8-bit 4:2:2 YCbCr with discrete outputs

The problem/question I have relates to VBLK. I thought that the TVP5150AM1 was compliant with the BT.656 specification. Hence I expected the vertical field blanking changes to be as:

  • Field1, Line 624 up to and including Line 22 e.g. 24 lines
  • Field2, Line 311 up to and including Line 335 e.g. 25 lines
  • Giving a total number of 'active' lines of 576 (625 - 24 - 25).

However, I am seeing VBLK give a total of 579 active lines. On closer inspection of the data sheet it shows

  • Field1, Mid-Line 624 up to and including Mid-Line Line 22 e.g. 23 lines
  • Field2, Start Line 312 up to and including Line 334  e.g. 23 lines
  • Giving a total number of 'active' lines of 579 (625 - 23 - 23).

This anomaly appears to give the USB UVC interface a problem, as it is programmed for PAL as interlaced 720 x 576 (e.g. two fields of 720 x 288), whereas the TVP5150AM1 is giving out 720 x 579.

How can the TVP5150AM1 be BT.656 compliant yet have the wrong vertical blanking fields?