LP-MSP430FR2476: Voltage drop on input with an external pull up

Thibaud HABRAND

Part Number: LP-MSP430FR2476
Other Parts Discussed in Thread: MSP430FR2475

Hello,

I am designing a product with a MSP430FR2475 microcontroller but in order to become familiar with the uc, I am using a LP-MSP430FR2476 .

I need to get the state of 12 IO in my project, so,as a test, I added an external pull up resistor on one input to see how the micro behaves. Seing that my system has to consumme as less as possible, I put a 1Mohm resistor as pull up, so it doesn't consumme too much when the I/O is putted to the ground.

But with a 1Mohm pull up resistor and powering the board by USB, I have a drop of voltage of 1.7V. Even with a 100kohm resistor my voltage dropped about 300mV.

Wanting to power up my microcontroller with some 2.2V I can't afford some big drops like those on my inputs.

I would like to know if you have any advise on how to reduce those drops, may be a soft features or anything.

Best regards,

Thibaud HABRAND, AXEM Technology

1Mohm resistor.

100kohm resistor.

over 1 year ago

0 Bruce McKenney47378 over 1 year ago

Guru 88410 points

This sounds like a bus conflict. What is that pin connected to? And how is it configured in your software?

0 Jace H over 1 year ago in reply to Bruce McKenney47378

TI__Guru 56685 points

Hello Thibaud,

As Bruce mentioned, it sounds like something else is in circuit that is causing the voltage division. Alternatively, you can setup the GPIOs to be an input with a pull up resistor (or down). This maybe a better solution for you.

+1 David Schultz over 1 year ago

Guru 18785 points

It is the input impedance of your scope that is creating a voltage divider. The results are consistent with that status display of "Impedance 1M".

0 Thibaud HABRAND over 1 year ago in reply to Bruce McKenney47378

Prodigy 10 points

Hello Bruce, thank you for your reply.

I configured my soft like that :

-Disable wdt

-Init clock

-mapping every GPIO as output (same issue even without this step)

-mapping GPIO 1.0, 1.1, 1.2, 1.3, 1.6, 1.7, 2.0, 2.2, 2.3, 3.0, 3.1, 3.3, 3.4 as output

-init UART with pins 1.4 and 1.5

- init UART with pins 2.6 and 2.5

- init SPI with pins 3.2, 3.5, 3.6 and 2.7

- Disable GPIO power on-default

0 Thibaud HABRAND over 1 year ago in reply to Thibaud HABRAND

Prodigy 10 points

I can show GPIO registers when I am debugging if you want.

0 Thibaud HABRAND over 1 year ago in reply to David Schultz

Prodigy 10 points

Hello David, thank you for your help. I recalibrated my probe and the results are much better.

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LP-MSP430FR2476: Voltage drop on input with an external pull up