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DS90UB935-Q1: frame sync frequency has a little offset

Part Number: DS90UB935-Q1

Dear team,

My customer use internal frame sync for 935&960, and their setting is as below, 

The total period of the FrameSync is (1 sec / 30 hz) / 600 ns or approximately 55555 counts.
For a 10% duty cycle, set the high time to 5555 (0x15b3) cycles, and the low time to 50000 (0xC350) cycles.

But when they test the frame sync signal at the camera side, the frequency is not exact 30Hz but 29.99Hz~30.01Hz. Is this normal phenomenon?

In addition, when setting 960's register 0x21=0x03(Round robin forwarding enabled), the screen display normally. But when I change to 0x21=0x28(Synchronous forwarding with line interleaving), the screen can't display. If we use Synchronous forwarding with line interleaving, the camera needs to be changed to external sync mode which means that camera only sends out data after receiving frame sync signal, right? Currently the camera can send out the data once powered on.

If 960 choose Synchronized CSI-2 Forwarding mode, 960 must send the frame sync signal to the camera, right?

Thanks & Best Regards,

Sherry

  • Hi Sherry,

    The frame sync signal is generated based on the refclk input. If there's ppm or deviation in the refclk, the frame sync signal will also have slight variation.

    When you do synchronous forwarding, you need to make sure the cameras are identical, and the frames are arriving at the same time. If the cameras are not synchronized, synchronous forwarding will show errors.

    Best,

    Jiashow