How to disable and enable UART at runtime?

[Yusuke]

I want to disable and enable UART at runtime. I don't use DMA and interrupt.

I read this thread.
https://devzone.nordicsemi.com/f/nordic-q-a/52496/nrf9160-uart-pull-up-and-power-consumption/216096#216096

I tried this code but doesn't work. Any help?

#define TXD_PIN 24

void enable_uart(){
	NRF_UARTE3->ENABLE = 8;
	NRF_UARTE3->TASKS_STARTTX = 1;
	NRF_UARTE3->TASKS_STARTRX = 1;
}

void disable_uart(){
	NRF_UARTE3->TASKS_STOPRX=1;
	while(NRF_UARTE3->EVENTS_RXTO == 0);
	NRF_UARTE3->EVENTS_RXTO = 0;

	NRF_UARTE3->TASKS_STOPTX = 1;
	while(NRF_UARTE3->EVENTS_TXSTOPPED == 0);
	NRF_UARTE3->EVENTS_TXSTOPPED = 0;

	NRF_UARTE3->ENABLE = 0;
	NRF_UARTE3->PSEL.TXD = 0xFFFFFFFF;
	NRF_P0_NS->OUTCLR = (1 << TXD_PIN);
}

Thanks!

[Martin Lesund]

Hi Yusuke,

Have you tried one of the other UARTS instead, like in the thread you linked to?

Do you have a logic analyzer to actually connect to the pins appointed to the UART pins?

[Yusuke]

This works out.

void enable_uart(){
	NRF_UARTE3->ENABLE = 8;
	NRF_UARTE3->TASKS_STARTTX = 1;
	NRF_UARTE3->TASKS_STARTRX = 1;
}

void disable_uart(){	
	NRF_UARTE3->TASKS_STOPRX=1;
	while(NRF_UARTE3->EVENTS_RXTO == 0);
	NRF_UARTE3->EVENTS_RXTO = 0;

	NRF_UARTE3->TASKS_STOPTX = 1;
	while(NRF_UARTE3->EVENTS_TXSTOPPED == 0);
	NRF_UARTE3->EVENTS_TXSTOPPED = 0;

	NRF_UARTE3->ENABLE = 0;
}

However, when I add these lines to the above disable_uart, it fails. Why?

    NRF_UARTE3->PSEL.TXD = 0xFFFFFFFF;
    NRF_P0_NS->OUTCLR = (1 << TXD_PIN); // TXD_PIN = 24

[Martin Lesund]

Hi Yusuke,

Wouldn't it make more sense to have the two lines at the end of disable_uart?

e.g.

void disable_uart(){	
	NRF_UARTE3->TASKS_STOPRX=1;
	while(NRF_UARTE3->EVENTS_RXTO == 0);
	NRF_UARTE3->EVENTS_RXTO = 0;

	NRF_UARTE3->TASKS_STOPTX = 1;
	while(NRF_UARTE3->EVENTS_TXSTOPPED == 0);
	NRF_UARTE3->EVENTS_TXSTOPPED = 0;

	NRF_UARTE3->ENABLE = 0;
	NRF_UARTE3->PSEL.TXD = 0xFFFFFFFF;
    NRF_P0_NS->OUTCLR = (1 << TXD_PIN); // TXD_PIN = 24
}

Best regards,

Martin L.