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LMH1980MMEVAL: TOF not syncing to reference input signal

Scott Heimendinger
Prodigy 30 points
Part Number: LMH1980MMEVAL
Other Parts Discussed in Thread: LMH1982

The TOF pulse output on my LMH1982 eval board does not sync to my reference input signal, apparently no mater how I have the settings configured on the board.

For my scenario, I have an incoming 1080/25p SDI video signal being generated from a video camera. My goal is to have a TOF pulse that is driven from this incoming signal.

I have inverted the polarity of the TOF pulse and connected it directly to an LED which sits right in front of my camera. This shows me whether the TOF pulse remains locked in phase with camera's video signal. If the LED always appears illuminated in the same way (on/off/partial) then i know the TOF Pulse and the video frame rates are synchronized. However, that's not what's happening.

Instead, very slowly (over the course of 2-3 minutes), the illumination of the LED very slowly crawls down the screen vertically. This means that the video clock driving the TOF pins is not in sync with the incoming video signal. 

I've tried every combination of settings I can think of, but nothing seems to lock the TOF pulse to the incoming video signal.

What am I doing wrong?

Thanks very much,

Scott

  • 0
    TI__Mastermind 32575 points

    Scott,

    Try settings "Output Format Pixels per Line" to 960, since you're using "SD Clock" as the TOF Ref Clock.  

    TOF rate = 27 MHz / (960 * 1125) = 25 Hz.

    Also, once TOF is aligned, you should set both EN_TOF_RST and TOF_INIT to 0, and click WRITE.

    TOF_OFFSET can be set to adjust the position of the TOF pulse relative to the input VSYNC pulse.  Setting TOF_OFFSET=1124 should cause the pulse to align with Top of Frame/Line 1, like shown in Figure 4 in the datasheet (which assumes incoming H/V syncs are Negative polarity).

    Regards,
    Alan