CCS/CC2652P: UART RX receive noise data when rx pin float

yingtao jia

Expert 1280 points

Part Number: CC2652P

Tool/software: Code Composer Studio

Hi, I use CC2652P, CCSv10.1, SDKv4.20.

My target board use DIO13 and DIO12 on uart communicate.

I tried 4 combinations as below:

(1) UART0, TX DIO13, RX DIO12

(2) UART0, TX DIO12, RX DIO13

(3) UART1, TX DIO13, RX DIO12

(4) UART1, TX DIO12, RX DIO13

The common issus is :

RX pin receives noise data continuously and thus triggers interrupt continuously when rx pin is float.

When I connect rx pin to an external uart module's tx pin, the rx pin stays silent, no noise data anymore.

Then, I disconnect rx pin , leave rx pin float, noise data appears again.

When rx pin is float, I check rx pin's voltage level with an oscilloscope, and find it low(0 V). In general, uart rx pin should be high when no data transfer.

And, when oscilloscope's probe touches the rx pin, noise data disappers, when the probe taken off, noise data comes.

When I connect rx pin to the external uart module's tx pin, the rx pin keeps high when I use the oscilloscope, and no noise data.

So I guess, there is no pull up on rx pin in the internal CC2652P , and this pin is high resistance state.

How to solve this issue please?

over 5 years ago

0 IUsedToBeARealPerson (M-W) over 5 years ago

TI__Guru 58425 points

Hi Yingtao,

There is no pull-ups mounted on the board, you either have to manually enable the internal pull-ups in software or on the board if you intend to have the UART running while not being connected to anything else.

On how to do this in SW, please see the following DriverLib documentation (more precisely IOCIOPortPullSet()):

dev.ti.com/.../group__ioc__api.html

0 yingtao jia over 5 years ago in reply to IUsedToBeARealPerson (M-W)

Expert 1280 points

Thank you.

Enable pull-ups in software helps.

I think pull up config should be done in SDK.

Maybe this issue will be fixed in next SDK release.

0 IUsedToBeARealPerson (M-W) over 5 years ago in reply to yingtao jia

TI__Guru 58425 points

Hi Yingtao,

Glad to hear it helped you get running.

I will make sure to forward your concerns but the reasoning behind the configuration is to avoid enforcing internal pull-ups. This as it is typically better (and preferred) to have the externally mounter pull-ups which allows you to set the strength of them in relation to what your need is to get the lowest current possible (among other things).

Bluetooth®︎

Bluetooth forum

CCS/CC2652P: UART RX receive noise data when rx pin float