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DS90UB954-Q1: Difference between FrameSync and GPIO forwarding

Part Number: DS90UB954-Q1


I want to forward a ECU frame sync signal to my sensor.

My ECU uses a DS90UB954 and my sensor a DS90UB953.

I understand that I can forward one of four GPIO signals from the 954 to the 953 (e.g. for SPI). I also understand that there is an internal framesync generator in the 954.

But if I use an external frame sync signal coming in via a GPIO pin and going out as via GPIO pibn, why do I have to route this via a framesync signal as stated in ?

Is there besides the GPIO backchannel transport also a framesync signal transport? Why should I use the latter before the primer?

Best regards.

  • Hello Juergen,

    You need to define in the DES that the incoming signal on that specific GPIO is a FrameSync signal.

    For example if you want to get External FrameSync signal from MCU into DES GPIO3, you need to configure the following:

    0x0F[3] = 1            #Define GPIO3 as Input

    0x18[7:4] = 1011   #External FrameSync on GPIO3

    0x6F[7:4] = 1010   #Determines the data sent into GPIO3 for the port back channel, is a FrameSync Signal

    On the SER, you need to configure followings:

    0x0E[7] = 1         #Define GPIO3 as output

    0x0D[7] = 1         #Enable remote deserializer GPIO3 data on local GPIO3

  • Hello Hamzeh,

    thank you for your answer. 

    Q1: Why should I not just route a GPIO3 via setting 0x18[7:4] = 0011?

    Q2: Is the "external framesync" mechanism just a toggling GPIO or is there more magic behind this?

    Q3: Does a "framesync" have lower jitter than "GPIO" or does framesync automatically sychronize the backchannel and forward channel?

  • Hello Juergen,

    1) sure, you can route GPIO3 as you want.

    2) There is no magic. It is just toggling GPIO.

    3) No, it does not have lower jitter, and it does not automatically synchronize the back channel and forward channel.

  • Just for documentation I made a 10.000 measurement statisitic with a 30cm cable.