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Incorrect TMDS clock frequency on ADV7481

Category: Hardware
Product Number: ADV7481

When receiving HDMI on the ADV7481, I am seeing results in the TMDS clock registers (HDMI 0x51 and 0x52) that do not match the values that I would expect.

For example, when capturing 1280x720 at 60Hz, I would expect the pixel clock to be 74.25MHz.  However, with a signal generator set to 720p60 output, I see 0x2e and 0x69, which I make to be 46+105/128 ie. 46.8203125MHz.  With a laptop, also set to 720p60 output, I see 0x25 and 0x21, which I interpret as 37+33/128 ie. 37.2578125MHz.

According to the AVI infoframes, the signal generator is outputting YUV444 and the laptop is outputting RGB.  Switching the laptop's output between 16 bit and 32 bit has no apparent effect on the value in registers 0x51-0x52.

Please clarify the meaning of the value that I am reading, and how I can use this to determine the actual pixel clock.