Cant set a pull-up in a GPIO

[jose_au_zone]

Hello! I'm trying to set a GPIO with a pull-up resistor, but I am always reading zero from the pin, no matter the input value

I'm configuring it like this:

	gpio_pin_config_t config;

	config.direction = kGPIO_DigitalInput;
	config.interruptMode = kGPIO_NoIntmode;

	GPIO_PinInit(GPIO2, 9U, &config);

	IOMUXC_SetPinMux(IOMUXC_GPIO_B0_09_GPIO2_IO09, 0U);

	IOMUXC_SetPinConfig(IOMUXC_GPIO_B0_09_GPIO2_IO09, 0x90B0U);

I've got the value 0x90B0 from the code generated by the pin config tool
If you look at page 693 of the reference manual, that should set a 100kohm pull-up
I've tried with 22kohm and 47k as well to no avail.
Is there anything I'm missing here?
This pin is connected to a switch that when pressed shorts the pin to the ground, so when the switch is not pressed it should read 1, right? But I'm always reading zero

Any help will be greatly appreciated

[jose_au_zone]

Thank you so much, that worked!
So, for the pull up to work, both the PKE and the PUE fields need to be enabled?
I get why the PUE field is necessary, but why the PKE?
According to this doc: https://www.nxp.com/docs/en/application-note/AN5078.pdf
The PKE is used to maintain the value just when the driver is disabled. What does "driver" mean exactly in this context? Isn't a GPIO set as an input with a pull-up an "enabled driver"?

Thank you so much!

[mjbcswitzerland]

Hi Jose

You need to read the description of the two bits more carefully - the descriptions are accurate, but not always that understandable.

A truth table makes is clearer:

                      Neither enabled  keeper enabled  pull-up/down enabled
IOMUXC_SW_PAD_CTL_PAD_PKE     0               1              1
IOMUXC_SW_PAD_CTL_PAD_PUE     x               0              1

Therefore PKE is always set if any of the two are needed.

Regards

Mark

[mjbcswitzerland · Accepted solution]

Hi

0x90b0 enables the keeper function.
0xb0b0 enables 100k pull-up.

Reference:
In the uTasker project the complete GPIO initialisation is done with one line:
_CONFIG_PORT_INPUT(2, PIN_GPIO_B0_09_GPIO2_IO09, (PORT_100k_PULLUP | PORT_SPEED_100MHz));

which removes the risk of such errors when using hex values rather than meaningful defines.

Regards

Mark
[uTasker project developer for Kinetis and i.MX RT]
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