5 years ago.

Redefine Serial UART tx pin

Hi,

For a SDI-12 protocol, I need to control TX pin in order to provide a pulse before sending actual command, that is used to wake-up the sensors.

I tried to setup a DigitalOut on TX pin, but it seems that the already configured Serial stops working.

Also tried to use HAL driver to switch between Normal and Alternate function, without success.

I am working with proprietary hardware, based on STM32L433 processor.

The Serial is a member of a class named SDI12_HalfDuplex , and is created in the constructor as in this:

class SDI12_HalfDuplex 
{
public:
    SDI12_HalfDuplex(PinName tx, PinName rx);

    void SDI12_HalfDuplex::SendBreak();
 .... other members functions;

private:
    Serial      mUART;
};

in the implementation, I have:

SDI12_HalfDuplex::SDI12_HalfDuplex(PinName tx, PinName rx) :  mUART(tx, rx) {}

void SDI12_HalfDuplex::SendBreak()
{
    DigitalOut tx(SDI_TX);
    tx = 0;
    wait_ms(15);
    tx = 1;
    wait_ms(10);

// WHAT TO DO HERE in order to have mUART working again ???

   return;
}

This doesn't work as mUART becomes unusable after redefining tx as digital output.

Using a dummy sending of a null byte, makes the SDI-12 interface work, but not with all sensor types as the minimum break time is not achieved.

Any help will be much appreciated.

BR, Carlos Paiva