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DS90UB928Q-Q1: Decode DS90UB928Q-Q1 cause black screen

Part Number: DS90UB928Q-Q1

encoded DS90UB927QSQE,Decode  DS90UB928Q-Q1;The whole machine starts normally and enters the radio interface,And then two seconds into the reverse,  after Back-up camera video,So repeat it for about 2 hours. the Whole unit black screen. beyond retrieve.Sometimes the read register goes wrong and sometimes the video stream is normal.

  • Hello,
    Can you verify your power up sequence and make sure the requirements in the datasheet are met? Also, what is your overall system power up sequence? Is the serializer powered up properly and up and running and sending data before the deserializer is powered up?

    Does a reset help recover from this state?
  • power up sequence is OK

    Reset 927(0X01=0X02) Can't recover, but RESET 928(0X01=0X02) can recover,

    Here is the Block Diagram, When video switches,the output CLK of TW8836 don't change,927 and 928 Power is OK,the LOCK of 928 is stable.

  • Hi what is your issue here? the display panel is becoming black after camera module is running or after 2hours operation?

    best regards,
    Steven
  • Hi Steven:
    A black screen appears when switching the video source of TW8836,software simulation 2 seconds switch,the camera module works all the time,the switch can't be recoved when black screen appears,but reset 928 is OK.
  • The display panel is becoming black after operating steps :2S input the CVBS signal, then cut down,after 2s input the CVBS signal again...
    We are compared normal and black screen ' registers : 1), DS90UB928 ' 0x3B 0x00 change 0x01; 2), DS90UB927 ' 0x0a 0x02 change 0x00;
    0x0c 0x07 change 0x05.
  • Hi,

    you means the input signals to UB928 is intermittently (every 2s)?

    if yes, the EQ of UB928's reg0x3B data value has no problem. and the link should have no any issue. 

    For your case, it seems the BIST of the link is trigged. please test the hardware pin signal of BIST to check whether the chipset is worked at BIST mode.

    best regards,

    Steven 

  • When a black screen appears, We test the UB928's BIST PIN is low all the time. please give us effective advice . Like this to solve the problem, the lily is getting cold.
  • You can debug this issue from system-level to get the root cause:

    1. for high speed link, when the video input is switching, please check whether the serializer and de-serializer work at normal mode: as a thumb of rule, you can measure the UB927 lvds clock input and UB928 LVDS clock output when issue is reported, are they synced? and what is the freq. (right or wrong)?

    2. UB927/UB928 provides diagnostic function, such as data pattern generation, when the display panel is black. also you can try to use internal clock and external clock & timing for pattern generation test. then you can make next actions.

    3. For BIST test, please check what is the BIST signal when you are switching input video?

    4. for SerDes link, it is sensitive on clock variation or jump. whether the input signal has different resolution? can you try whether resetting UB927 would make the link well?

    Steven

  • Thank you for your support. But We've tried all the advice you gave us. the CLK is exactness(48MHz),BIST signal keep low level all the time.....,Can we actually analyze it?
  • Please provide the debug records based on above tests. For example, what is the result if you reset the UB927 when you switched the input signals (which is recommended for high speed serdes link). From the chip level, we don't see any clues on your issue. thanks.

    Steven