Unable to receive on Rx pin because Tx is always high.

[Shubham]

I have a custom board. It has its Tx and Rx combined into one wire bus. I am able to transmit data on the bus. But I am unable to receive any data on the board. This is because of circuit design.

In order to receive data I thought of disconnection the Tx pin when I am done transmitting the data. I did it by adding some code in `$SDK_ROOT/modules/nrfx/hal/nrf_uart.h`.

__STATIC_INLINE void nrf_uart_tx_pins_disconnect(NRF_UART_Type * p_reg)
{
#if defined(UART_PSEL_TXD_CONNECT_Pos)
    p_reg->PSEL.TXD = NRF_UART_PSEL_DISCONNECTED;
#else
    p_reg->PSELTXD = NRF_UART_PSEL_DISCONNECTED;
#endif
}

I thought of calling this function when I am done transmitting and want to receive data. This is works partially.

When I transmit and disconnect tx pin then I do not receive any data. But If I do not send any data and directly try to receive it works.

I want both way communication.

Is there anything to turn off Tx completely and just wait for receive, and when I want to transmit I enable the Tx and starts sending.

[hmolesworth]

From the manual "PSEL.RXD, PSEL.RTS, PSEL.RTS and PSEL.TXD must only be configured when the UARTE is disabled.". The Uart has to be disabled before changing the Tx pin then re-enabled.

[Shubham]

I am doing all the actions between `nrf_uart_disable` and  `nrf_uart_enable`.

[hmolesworth]

So you have this, right? You sure you are turning the pin back to an input as well as disconnecting from the Uart?

  nrf_uart_disable();
  p_reg->PSEL.TXD = NRF_UART_PSEL_DISCONNECTED;
  // Pin now disconnected from Uart, but it's still an output pin so must also turn off output drivers
  nrf_gpio_cfg_default(p_reg->PSEL.TXD);
  nrf_uart_enable();

[Shubham]

I am calling `nrf_uart_tx_pins_disconnect` between `nrf_uart_disable` and `nrf_uart_enable`

__STATIC_INLINE void nrf_uart_tx_pins_disconnect(NRF_UART_Type * p_reg)
{
    nrf_gpio_pin_clear(17);
#if defined(UART_PSEL_TXD_CONNECT_Pos)
    p_reg->PSEL.TXD = NRF_UART_PSEL_DISCONNECTED;
#else
    p_reg->PSELTXD = NRF_UART_PSEL_DISCONNECTED;
#endif
}

Let me try turning that pin to an input.

[Shubham]

In your code p_reg->PSEL.TXD will be 0xFFFFFFFF so I guess it wont have any effect.
I guess nrf_gpio_cfg_default should be passed with actual pin number.

[hmolesworth]

Yes, good catch; I meant to either set the pin to default input before releasing from the uart or indeed use the correct pin number (which wasn't given in your post) in the order shown. I would advise setting the pull-up as well, as with the default config the pin will float which could cause issues with the remote device when the remote device reverts to listening to Tx which will float potentially low and look like spurious transmitted data without a pull-up.

  // Use p_reg->PSEL.TXD as we don't know which pin is being used
  nrf_uart_disable();
  // Pin is an output pin so must turn off output drivers - maybe also make enablee pull-up
  nrf_gpio_cfg_default(p_reg->PSEL.TXD);// Release pin
  p_reg->PSEL.TXD = NRF_UART_PSEL_DISCONNECTED;
  nrf_uart_enable();

Anyway did it work?

[Shubham]

nope it did not work out.