MSP430F67791A: UART RX Line (P4.1) starts pulling down on some chips

Afzaal Ameer1

I have come across this weird behaviour on multiple boards where P4.1 which is being used for UART switches to pulldown mode after running fine for sometime. And it's repeatable on 2 out of 4 boards I have tested. Any pointers on what might be causing this ?

over 5 years ago

0 Srinivas Lingam over 5 years ago

TI__Expert 7395 points

Hi Afzaal,

Were you trying to attach an image with your post?

Is there something in your SW that could be reprogramming the P4 control registers? Is it possible to see the state of the registers P4DIR.1 P4SEL0.1 P4MAP.1 to explain the behavior?

Srinivas

0 Afzaal Ameer1 over 5 years ago in reply to Srinivas Lingam

Prodigy 140 points

There is really nothing that changes any registers after initialising. I monitored the registers and they don't change.

Image of TX and RX lines.

0 Bruce McKenney over 5 years ago in reply to Afzaal Ameer1

Guru 102865 points

Is anything connected to the (Rx) pin? If not, it will be floating since the UART will only drive its Tx pin.

0 Afzaal Ameer1 over 5 years ago in reply to Bruce McKenney

Prodigy 140 points

Yes. And as mentioned, it works for sometime and then pulls down. Sometimes in minutes, sometimes after an hour from boot.

Zoomed out view

0 Bruce McKenney over 5 years ago in reply to Afzaal Ameer1

Guru 102865 points

All the same, I would describe that as "drifting" down -- "pullling" down would be somewhat more abrupt, and you probably wouldn't see that cross-talk from the Tx pin.

What's at the other end of the wire? Can you probe there?

**Attention** This is a public forum

MSP low-power microcontrollers

MSP low-power microcontroller forum

MSP430F67791A: UART RX Line (P4.1) starts pulling down on some chips