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DS90UB914A-Q1: Resume Valid Output After Reconnect a Cable

Part Number: DS90UB914A-Q1
Other Parts Discussed in Thread: DS90UB913A-Q1

[ DS90UB914A-Q1 ] Resume Valid Output After Reconnect a Cable

Hi,

My customer has reported that some of their ECUs (DS90UB914A-Q1 mounted) does not resume the output, even though a camera cable is connected again.
Here is the result.

- Let camera(DS90UB913A-Q1) and ECU work as normal
- Disconnect FPD-Link III cable. DS90UB914A-Q1 goes into loss of lock condition, output signal is no longer valid.
- Re-connect cable
- Some of ECUs resume the valid output, but some other does not resume.

Can you comment on this which shows different behavior?


I have adviced customer that a reset with either PDB or I2C is recommended after event of cable disconnect and loss of lock.





Thank you for your support in advance.
Regards,
Ken

  • Hi Ken,

    Your advice is correct, digital reset is needed after loss of lock or cable disconnect/connect to ensure consistent startup condition. 

    Disconnect cable during device operation is not normal condition, it may put the device into unknown state. 

    Sincerely,

    Charley Cai

  • Hi Charley,

    Thank you for your reply!
    I have been talking with customer and had new information as below.

    - Let camera(DS90UB913A-Q1) and ECU work as normal
    - Set "BC Enable bit to 0", i.e. back-channel is disabled.
    - Disconnect FPD-Link III cable. DS90UB914A-Q1 goes into loss of lock condition, output signal is no longer valid.
    - Re-connect cable
    - Some of ECUs resume the valid output, but some other does not resume.



    Accodring to customer, they set BC Enable (0x01[2]) to 0. This means that the back-channel communication is disabled.
    When camera cable is disconnected, the power supply to DS90UB913A-Q1 is also cut off. (Because they use PoC)

    So, when cable is re-connected and power supplied again, the required initialization between DS90UB913A-Q1 and DS90UB914A cannot be performed.
    Thus the link between devices cannot be establised.

    This is what I understand from information and datasheet. Do you have any other aspect?

    Thanks,
    Ken

  • Hi,

    Back channel disabled is unlikely the issue here. More likely the issue is with disconnecting the cable. 

    When cable is disconnected, it is possible for 914A to latch on an unexpected state that may cause no output. That's why it is always recommended to perform a reset to ensure correct startup condition. 

    Sincerely,

    Charley Cai

  • Hi Charley,

    Thank you for sharing your thought, it's helpful.

    Let me make sure one thing.
    Even though the back channel is disabled with BC Enable bit(0x01[2]), can initialization (or kind of hand-shake after power-up) between DS90UB914A-Q1 and DS90UB913A-Q1 be successfully performed?

    Do you recommend customer to disable the back channel communication?

    Thanks,
    Ken

  • Hi Ken,

    Yes, the synchronization (hand-shake) between 913A and 914A is done through forward channel. The back channel communication contains I2C commands and GPIO data. 

    If back channel is disabled there won't be any I2C communication between 914A, 913A and remote sensors. It is generally not recommended. 

    Sincerely,

    Charley Cai

  • Hi Charlet,

    Thank you for your support!
    We have performed quick lab experiment with 913A/914A EVM.
    See our findings below. As you said, we cnofirmed that LOCK can be achieved even with 0x01[2] = 0.

    Case 1
    1: Power up both 913A and 914A EVm as default and confirm LOCK LED of 914A EVM is on
    2: Change 0x01[2] to "0", then confirm LOCK LED of 914A EVM is still on
    3: Diconnect FPD-Link cable from 913A EVM, then LOCK LED of 914A EVM is turned off
    4: Re-connect FPD-Link cable, then confirmed LOCK LED of 914A EVM is turned on again.

    Case 2
    Same steps from 1 through 3 as above
    4: Perform device reset with changing 0x01[0:1] to "1"
    5: 0x01]2] is backed to its default value "1", then set this to "0"
    6: Re-connect FPD-Link cable, then confirmed LOCK LED of 914A EVM is turned on again.

    Here, I need your help.
    We now know that lock can be achieved. However, what about mode settings?
    From the datasheet, mode setting is loaded from 914A to 913A through back channel.
    Such as, 914A is configured as 12bit, while 913A is 10bit mode with hard strip, this kind of different settings.
    Our experiments cannot reveal this difference.

    Thanks,
    Ken

  • Hi Ken,

    The 914A could program 913A into the correct mode through forward channel only when back channel is disabled. This could be monitored using register 0x1F on 913A. 

    There is no mode strapping on 913A to select 10bit/12bit mode.  The mode pin on 913A is used for selecting device operation with PCLK or external clock. 

    I will have to get back to you on the datasheet description. 

    Sincerely,

    Charley Cai