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DS90UB936-Q1: The Internally Generated FrameSync problem

Chris Liu
Prodigy 210 points
Part Number: DS90UB936-Q1


Hi,

I use Internally Generated FrameSync to sync rxport0/1 image, the framesync signal needs to have 1% duty.

The circuit is designed to use 4Gbps FPD-Link so the back channel rate needs to configured to 50 Mbps.

For 30fps image, I need to generate 30Hz frame sync signal, the high time and low time will be 

1000000000*0.01/600/30 = 555.5556
1000000000*0.99/600/30 = 55000

The problem is when using 20fps image, to generate 20Hz, the high time and low time will be 

1000000000*0.01/600/20 = 833.3333
1000000000*0.99/600/20 = 82500

The 2 bytes FS_LOW_TIME can't fulfill the number 82500.

How to solve this problem? 

Thanks.

  • 0
    TI__Guru 66910 points

    Hi Chris, 

    Since today is a US holiday for TI, we will review your question and get back to you on Monday 4/18. Thanks for your patience. 

    Regards,

    Logan

  • 0 in reply to Logan Cummins
    TI__Guru** 103215 points

    Hello Chris,

    There are a few options:

    1. Use non-synchronous mode with the 935 which would be 10Mbps BC instead of 50Mbps. This would increase the unit time of the frame period

    2. Use synchronous half rate mode with the 935 (set the BC to 25Mbps which will drop the FC of the 935 to 2Gbps instead of 4Gbps. This will limit allowable CSI-2 throughput to 1.6Gbps instead of 2.528Gbps. But it will also increase the BC frame period 

    3. If you can get away with 50% duty cycle, use the high/low mode which allows 3 bytes to set the frame sync period

    Best Regards,

    Casey