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Original question:

DS90UB926Q-Q1: Interfacing with DS90UB947 deserializer over single lane FPD-Link

DS90UB926Q-Q1: using GPIO/GPO functionality for PWM

Bart
Expert 6310 points
Part Number: DS90UB926Q-Q1

Hello,

we do have some other questions regarding DS90UB947->DS90UB926.

We need GPIO/GPO functionality on deser side. We have previously used ds90ub948 with its high speed (direct) GPIO’s to control PWM input of backlight driver.

With ds90ub926, it’s another story as I can see, since it has only GPO_REG, which are only controlled through registry and would thus cause large overhead if we try to transfer PWM through FPD-Link.

Is there any TI recommended way to utilize DS90UB926 GPO’s for PWM functionality, and not cause overhead in FPD-Link packages?

Thank you.

  • 0
    TI__Guru* 98455 points

    Hello Bart,

    If you use DS90UB926-Q1 in 18 bit mode, there are some pin controlled GPIO available (shared with the data pins). However if this is not an option then unfortunately there is no other method. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 6310 points

    Hi Casey,

    we have found this document: http://www.ti.com/lit/an/snla234/snla234.pdf

    It says that it is possible to configure GPIO8, GPIO7 and GPIO6 (I2S pins on DS90UB926) for DS90UB925-DS90UB926 Direction as GPIO regardeless of 24 or 18 bit?

    It also states that it is possible to use them in static operation as GPO_REG (so only as outputs and only by writing in registry).

    This is a bit confusing, since datasheet suggest that GPIO functionality can be used only in 18-bit mode (for pins 27,28,40,41. These pins are different pins than those above-mentioned, they are part of RGB IF).

    I2S pins (1,30,45,18 and 19) GPO_REG[8:4] are said by datasheet to only be outputs that are set by configuration register.

    • Which of the above is true?
    • If the first document and statement is true, is it possible to use ds90ub926 in that configuration with ds90ub947 serializer?

    Thank you.

  • 0 in reply to Bart
    TI__Guru* 98455 points

    Hello Bart,

    Apologies for the confusion - I should not have assumed that you were also using I2S. If you are not using I2S, then you can follow the app note to enable more GPIOs in 24 bit mode. It should work with 947. 

    Best Regards,

    Casey 

  • 0 in reply to Casey McCrea
    TI__Expert 6310 points

    Hi Casey,

    thanks, this is good news. Does it mean we can also use these GPIO's for PWM functionality (for direct PWM driving of backlight driver IC)? Meaning, are they capable of high speed operation?

    Kind regards

  • 0 in reply to Bart
    TI__Guru* 98455 points

    Hello Bart,

    Please refer to the app note you mentioned for speed limitations of these different pins. Some of the pins speeds depend on the PCLK for the system.

    Best Regards,

    Casey