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ADV7611 FreeRun mode 1

Question asked by acebrian on Nov 25, 2011
Latest reply on Nov 17, 2016 by danpianji88

We have designed a board that includes an ADV7611 connected to a MPEG2 encoder.

 

The MPEG2 encoder has a D1 8-bit parallel with embedded SAV/EAV video input interface that only supports pixel clock from 27 MHz to 36 MHz. In fact this is PAL 720x576i or NTSC 720x480i ITU BT.656 compatible interface.

 

We have configured the ADV7611 to get 8-bit SDR ITU BT.656 when HDMI input is 576i using the configuration script from http://ez.analog.com/message/35184#35184

 

If the external HDMI transmitter (i.e: DVB-T receiver) outputs HDMI 576i then the board works fine.

 

If the external HDMI transmitter outputs HDMI 576p, 720p, 1080i or 1080p then the board doesn’t work. This is the expected result because the ADV7611 cannot downscale video resolution and cannot convert from progressive to interlaced video.

 

The problem is that we need some way to block HDMI 576p, 720p, 1080i or 1080p at the ADV7611 output because these video resolutions use a pixel clock higher than 36MHz and they hang our MPEG2 encoder.

 

The first approach has been EDID editing in order to only allow external HDMI transmitter to use 576i and 480i. But we have found that some low cost HDMI transmitters discard EDID information especially during startup.

 

The second approach has been using FreeRun mode 1 with 576i 50Hz HDMI-COMP:

 

  {0x98, 0x00, 0x01}, // Video standard 576i

  {0x98, 0x01, 0x15}, // Primary Mode HDMI-COMP, 50Hz

  {0x44, 0xBA, 0x03}, // Set HDMI FreeRun mode 1

 

This second approach seems to correctly block 720p, 1080i and 1080p because they use a video resolution higher than 720x576 and therefore the ADV7611 switch to FreeRun mode (we see the blue screen). But 576p isn’t blocked because it uses the same 720x576 resolution as 576i and therefore the ADV7611 doesn’t switch to FreeRun (we see garbage screen because pixel clock is 54 MHz and our MPEG2 encoder cannot handle it).

 

Is there any way to configure the ADV7611 to automatically switch to a 576i FreeRun if HDMI input is 576p, 720p, 1080i or 1080p? In fact, what we need is to ensure that the ADV7611 will output ALWAYS a 720x576i video resolution with a 27 MHz pixel clock.

 

Thanks.

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