Disabling internal pull up in Analog input pin for ADC

[Shafy]

Hi,

I have configured the IO09 as analog input pin for ADC in the i.mx6UL processor (myirtech mys-6ul board)

I am using the following pin configuration in the dts

pinctrl_adc1: adc1grp {
fsl,pins = <
MX6UL_PAD_GPIO1_IO09__GPIO1_IO09 0xb0
>;
};

But the issue is the pin in internally pulled up to 3.3V.  So when no external voltage is connected, ADC reading is giving the value 4095.   When external voltage is connected, it is causing the reading go wrong.  I have tried configuring the IO05 also with the same result.  I have confirmed that these pins are not used in any other configuration in the dts.

How can I disable the internal pull up  ?  I have tried the bias-disable = <1>; in the dts with no effect.

Can some one advise ?

Shafy

[josephlinares]

Hi,

Thank you for your interest in NXP Semiconductor products,

I think you can get started with this thread, likely there is an overlay between its use within other dtb or a driver that uses that pin.

You can run the tests that he ran, please provide the results.

Regards,

[Shafy]

@josephlinaresThanks for your reply.

I couldn't find an issue as suggested in that thread. I am not using the parameters he found issue with.

Do you have an overlay for adc that is tested and working in i.mx6ul ?

Thanks

Shafy

[josephlinares]

Hi,

It's for debugging, could you verify at userspace that the value isn't overwritten, but I'm attaching a presentation that will be more useful, could you verify the values for the GPIO to see that they're being changed?

Thanks,

Regards