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Original question:

DS90UB953-Q1: RTOS/TDA2PXEVM: Serializer and Sensor not getting detected using I2C Back channel

DS90UB913A-Q1: Using a low resolution camera with a low speed clock

Kevin Kinion54
Prodigy 120 points
Part Number: DS90UB913A-Q1
Other Parts Discussed in Thread: DS90UB913Q-Q1,

I am using a OVM6946, 400 x 400 camera with a OV426 interface IC.  I am using the serializer's external clock at 48MHz and returning 24MHz to the OV426.  I have two questions:  First, if there is no pixal clock initially, does the serializer still establish the FDP-III link as it claims on sheet 23 on the data sheet?  If so, what would be the expected frequency?  I am not seeing it with the oscilloscope.  Second, the pclk is only 8MHz.  Is that a problem?

  • 0
    TI__Genius 11340 points

    Hi Kevin,

    What do you mean by serializer's external clock at 48MHz and returning 24MHz to the OV426?

    I would have to get back to you on the first question, but I do not expect that a PCLK of 8MHz would work, since it is out of the range of our recommended operating condition:

    Best,

    Jiashow

  • 0 in reply to Jiashow Ho
    Prodigy 120 points
    Dear Jiashow,
    We had a 48 MHz Clock going into GPOI3/CLKIN of the Serializer and 24MHz on the GPIO2/CLKOUT.  The 24 MHz is connected to the OV426 which is the Omnivision camera interface IC.  The camera is connected to the OV426.  The OV426 returns a 8MHz PCLK which is slower than the 25MHz minimum as you said.  I sent a message to TI last may and asked this question and was given some assurance that this would work.  Why does the PCLK need a minimum 25MHz?  Is there anyway of making this work with the camera that we are using (8MHz pclk)?  If not, is there a serializer solution that will work?
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  • 0 in reply to Kevin Kinion54
    TI__Genius 11340 points
    Hi Kevin,

    Without the presence of PCLK, the serializer will establish FPD-Link using ~50/37.5MHz internal oscillator, but this oscillator is not very accurate at +/-25% tolerance.

    The reason why 8MHz PCLK won't work reliably is because back channel might get in the way. You might be able to get it to work by increasing blanking from your sensor to get higher PCLK.

    If you are using STP, you maybe optionally use the 913 instead, but even the 913 can only be supported with PCLK of at least 10MHz .

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    Prodigy 120 points

    Dear Jiashow,

    We are using the 913.  The full part number is DS90UB913ATRTVRQ1. On the other side we are using the 914 deserializer.  To which part are you referring?  Also, we are not using the back channel.  Is there a way of disabling the back channel?

  • 0 in reply to Kevin Kinion54
    TI__Genius 11340 points
    Hi Kevin,

    DS90UB913Q-Q1 supports STP only and DS90UB913A-Q1 supports both coax and STP. You are currently using the DS90UB913A-Q1, which requires PCLK of greater than 25MHz. The DS90UB913Q-Q1 requires PCLK of greater than 10MHz.

    You can disable the back channel by setting the second bit of register 0x01 (Reset) to 0.

    Best,
    Jiashow
  • 0 in reply to Jiashow Ho
    Prodigy 120 points
    We're going to try swapping the chips and disabling the back channel. I'm not sure about adding blanking from the sensor.
  • 0 in reply to Kevin Kinion54
    Prodigy 120 points

    I replaced the A version of the 913 with the Q version on the 913.  We only have a 8MHz pixel clock but it seems to work just fine.  We are getting nice video streaming image through the serializer/deserializer link.  We bypassed the I2C so are not using the back channel. We are considering changing to the DS90UB921 / DS90UB924 because the required pixel clock is only 5MHz.  Does this seem reasonable to you?

  • 0 in reply to Kevin Kinion54
    TI__Genius 11340 points
    Hi Kevin,

    It’s feasible but 92x maybe be overkill for a camera application, since you're only utilizing half the input b/w but running FPD link at double the linerate.

    Best,
    Jiashow