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Trouble in application to lmh1982

Simon WuC
Prodigy 30 points
Other Parts Discussed in Thread: LMH1982, LMH1981

Hi,All

    I am using lmh1982 with lmh1981 for video system design. There is one trouble block me for a long time. I list the problem and test result from my debug process as followed.

       The lmh1982 is used for generating synchronization clock matched with reference A or reference B as my program selection. In my application, ref A feed by lmh1981 and reference B derived from a SD-SDI (576i) geneartion module in FPGA which generate h&v followed the suggestion to choose to configure the FPGA to gate the V sync signal, allowing only the even field V pulses and gating off the odd field V pulses(available in datasheet page 16). But the h&v feed into reference B can not make lmh1982 work well when the out format frame rate is non 25Hz while the h&v from reference A(lmh1981 output) can work excellently.

In debug process, I have got some other phenomena and I pasted and hope it can help to find the root reason.

1st. when the sdi out format frame rate is 25Hz(1080i50) or 50Hz(720p50), it work normally While it go wrong as             sdi out format frame rate is 60Hz(720p60) and 30Hz(1080i60).

2nd. lmh1982 will out target tof and clock frequency when it select reference A as input, no matter what frame rate          is it.

3rd. Once the lmh1982 work well, the tof frequency is the same as output sdi format. If lmh1982 work unnormally,         the tof frequency will more than target sdi format.

eg. sdi format as 720p60, its frame rate is 60Hz, target frequency of tof is 60Hz, but it will be 65Hz when it does work badly.

     If sdi format as 1080i60, its frame rate is 30Hz, target frequency of tof is 30Hz, but it will be 35Hz when it does work wrong.

4st. After power on, lmh1982 may work normally several minutes sometimes, but go wrong finally.

Hope get guidance from you, Thanks First!

  • 0
    TI__Mastermind 32575 points

    Hello,

    Does the H/V timing recovered from SDI reference meet the DTHV spec, as described in reference frame decode section on pg. 16?

    When you program the output format timing, are you using Output TOF clock = 27 MHz for all output formats (e.g. "Option 2" pg. 20)?  Are you programming the correct reference frame timing and input-output frame rate ratio based on the reference H/V rate and output TOF rate?

    After you program output initialization sequence to align Output TOF to reference frame, are you clearing EN_TOF_RST and TOF_INIT bits?  If you don't clear these bits after the init sequence, it cause improper TOF and clock output operation.

    Regards,
    Alan