TM4C123GH6PGE: Enable internal pull-up resistors

Ayhan Evren

Part Number: TM4C123GH6PGE

Hello Everyone!

I am trying to enable internal pull-up resistors in the TM4C123GH6PGE on my custom board.

The purpose of this, I am addressing 10 multiplexers with PC 0-1-2-3 pins of the MCU. When I connected the Multiplexers to the MCU the address pins voltage level drops to 2.4V, and this level is not enough to enable addressing. I think the reason of this issue is current. It is not enough. That is why I tried to enable internal pull-up resistors of these 4 pins.

Datasheet of the Multiplexer which I used on the board:

https://www.mouser.com.tr/datasheet/2/916/74HC_HCT4067-1597878.pdf

First I set the PC 0-1-2-3 pins as GPIO and then I used below code to enable pull-up resistors but nothing has changed, voltage level is still 2.4V.

GPIOPadConfigSet(GPIO_PORTC_BASE, GPIO_PIN_3, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);
GPIOPadConfigSet(GPIO_PORTC_BASE, GPIO_PIN_2, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);
GPIOPadConfigSet(GPIO_PORTC_BASE, GPIO_PIN_1, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);
GPIOPadConfigSet(GPIO_PORTC_BASE, GPIO_PIN_0, GPIO_STRENGTH_2MA, GPIO_PIN_TYPE_STD_WPU);

Do you have any idea is this the right way to enable internal pull-ups for this MCU? And will it work for increase flowing current via these pins?

over 2 years ago

+1 Chester Gillon over 2 years ago

Guru 92251 points

Ayhan Evren said:
I think the reason of this issue is current.

The multiplexers are CMOS devices and the maximum input leakage current shown is ±2.0 μA. I.e. input leakage current shouldn't be an issue.

If the multiplexers don't have a VCC supply, the address pins from the TM4C123GH6PGE could be trying to power the multiplexers through the clamp diodes, which could be the problem.

How are the multiplexers and TM4C123GH6PGE powered?

0 Ayhan Evren over 2 years ago in reply to Chester Gillon

Prodigy 50 points

Hello Chester,

Multiplexers are pwered from their own VCC. No power goes from MCU to Multiplexers.

So that means the problem isn't occurred because of the current, I'll have to focus on another area on the board.

+1 Ralph Jacobi over 2 years ago in reply to Ayhan Evren

TI__Guru*** 128095 points

Hello Ayhan,

Have you unlocked these pins?

See this FAQ for details: https://e2e.ti.com/support/microcontrollers/arm-based-microcontrollers-group/arm-based-microcontrollers/f/arm-based-microcontrollers-forum/1020814/faq-how-to-get-locked-gpio-pins-on-tm4c123-devices-to-work

Best Regards,
Ralph Jacobi

0 Ayhan Evren over 2 years ago in reply to Ralph Jacobi

Prodigy 50 points

Hello Ralph,

Yes I unlocked the JTAG pins for GPIO with below code

HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x01;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfe;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x02;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfd;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x04;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xfb;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x08;
HWREG(GPIO_PORTC_BASE + GPIO_O_AFSEL) &= 0xf7;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = GPIO_LOCK_KEY;
HWREG(GPIO_PORTC_BASE + GPIO_O_CR) = 0x00;
HWREG(GPIO_PORTC_BASE + GPIO_O_LOCK) = 0;
GPIOPinTypeGPIOOutput(GPIO_PORTC_BASE, (GPIO_PIN_0 | GPIO_PIN_1 | GPIO_PIN_2 | GPIO_PIN_3));

By the way I tried the same procedure with different board and it worked. So the porblem was on my board not on the MCU.

Thanks for helping.

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TM4C123GH6PGE: Enable internal pull-up resistors