topic Re: RT1040 ADC issues in MCX Microcontrollers

RT1040 ADC issues

Xiao_Liu — Tue, 27 Jan 2026 05:49:47 GMT

Follow IMXRT1040RM ， disable GPIO keeper for ADC input signal。

if ADC input gpio is NC，ADC read value is abnormal，the NC input pin is 0V measured by multimeter.

we have another ADC channel which is connected to an NTC thermal sensor. the ADC read value is ok.

When i set ADC GPIO pin config as default(

IOMUXC_SetPinConfig(ADC_PIN, 0x10B0U)), this is set keeper enable as default, the ADC read value of input channel which is NC is nearly zero. it's work this time.

So, Should i disable Keeper function of GPIO for ADC input signal?

Re: RT1040 ADC issues

mayliu1 — Tue, 27 Jan 2026 11:01:38 GMT

Hi @Xiao_Liu ,

Thank you so much for your interest in our products and for using our community.

Regarding your question,

Yes. For ADC input pins, the keeper function should be disabled.

Please refer to NXP SDK demo PIN setting.

Please note that an ADC channel should not be left floating; if the pin is NC, the conversion result is undefined.
Enabling the keeper may make the reading look stable, but it is not a reliable or recommended solution.

Wish it helps you

Best Regards

MayLiu

Re: RT1040 ADC issues

Xiao_Liu — Wed, 28 Jan 2026 07:31:58 GMT

Hi,May:

The ADC is designed to be floated if module is not connected. the module is Optional.

Follow "ECKMIMXRT1040_ADC_12B1MSPS_SAR_POLLING" , the ADC input pin of GPIO_AD_B1_04 is set as keeper function disable.

the NC ADC input pin is measured as 0V, but ADC read value is 0.6 or 0.7V if keeper disable.

ADC read value is nearly 0V if keeper enable as default. by this way we can use ADC read value as module detection

So, what the side effect when keeper is enabled.

What should i do to read ADC input pin which is NC as we need auto detect of the optional module?

Re: RT1040 ADC issues

mayliu1 — Mon, 02 Feb 2026 02:23:54 GMT

Hi @Xiao_Liu ,

Thanks for your updated information.

Enabling the keeper on an ADC pin is not recommended. The keeper holds the last state, which can cause incorrect ADC readings and makes module detection unreliable.

For a stable and accurate result, we recommend adding an external resistor to set a clear default level when ADC is not connected.

Best Regards

MayLiu

Re: RT1040 ADC issues

Xiao_Liu — Tue, 03 Feb 2026 05:56:58 GMT

Hi,May
got it. we will use external pull up when ADC is not connected.
thanks for your help.

Re: RT1040 ADC issues

mayliu1 — Tue, 03 Feb 2026 06:07:16 GMT

Hi @Xiao_Liu ,

Thanks for your updated information.

If this post answers your question, please click the "Accept As Solution" button. Thank you!

Best Regards

MayLiu