How to add RS‑485 DE pin control to console/shell UART on nRF52840?

Question

Hello, 
 On my board I implemented an RS-485 interface using the ST4E1216IDT transceiver. The DE (Driver Enable) and RE (Receiver Enable) pins are tied together and connected to a pin (de pin) of the nRF52840, in order to act as a tx data enable pin. On my application I am able to use the RS-485 UART by setting the de pin HIGH just before transmission, and then LOW on UART_TX_DONE event. Using this, I have validated that by board is operational. 
 Bellow is a code snippet that described this operation: 
 /* UART Callback to handle transmission completion */
static void uart_cb(const struct device *dev, struct uart_event *evt, void *user_data)
{
 switch (evt->type) {
 case UART_TX_DONE:
 /* Set DE pin LOW when transmission is finished */
 gpio_pin_set_dt(&uart_depin_dev, 0);
 break;
 default:
 break;
 }
}

 // Set DE pin HIGH to enable the transmitter
 gpio_pin_set_dt(&uart_depin_dev, 1);

 // Start asynchronous UART transfer
 ret = uart_tx(uart, tx_buf, sizeof(tx_buf), SYS_FOREVER_MS); 
 
 What I would like to achieve is to connect the zephyr console and the shell on that UART (RS-485). In order to do that the UART should support a DE hw control pin, because the backend should change the state of the DE pin depending on transmitting or receiving, since the RS-485 is a half duplex serial protocol. 
 Is there a way to achieve the console and shell UART to have an RS-485 operation. 
 
 Thank you in advance 
 Avgerinos

Susheel Nuguru · Accepted Answer

You cannot make console/shell toggle the DE pin with nRF52840 without changes to the uarte driver and possible the dts property of the uarte. Maybe you can use an rs-485 with auto direction capability so that the uart part remains the same as what nordic chips can support.

mbakker · Answer

I had the same problem and managed to solve it using the PPI (DPPI on nRF54L). Simply connect the UARTE TX_READY to the SUBSCRIBE_SET and the TX_END to SUBSCRIBE_CLR of an unused GPIOTE instance. No need for any changes in the DT or drivers. Here's how I achieved it on the nRF54L, it should not be difficult to port to the nRF52: static int enable_uart_de(void) { // Assert P1.02/UART_DE when transmitting on UARTE21 NRF_UARTE21->PUBLISH_DMA.TX.READY = (1 << UARTE_PUBLISH_DMA_TX_READY_CHIDX_Pos) | (UARTE_PUBLISH_DMA_TX_READY_EN_Enabled << UARTE_PUBLISH_DMA_TX_READY_EN_Pos); NRF_UARTE21->PUBLISH_DMA.TX.END = (2 << UARTE_PUBLISH_DMA_TX_END_CHIDX_Pos) | (UARTE_PUBLISH_DMA_TX_END_EN_Enabled << UARTE_PUBLISH_DMA_TX_END_EN_Pos); NRF_GPIOTE20->SUBSCRIBE_SET[5] = (1 << GPIOTE_SUBSCRIBE_SET_CHIDX_Pos) | (GPIOTE_SUBSCRIBE_SET_EN_Enabled << GPIOTE_SUBSCRIBE_SET_EN_Pos); NRF_GPIOTE20->SUBSCRIBE_CLR[5] = (2 << GPIOTE_SUBSCRIBE_CLR_CHIDX_Pos) | (GPIOTE_SUBSCRIBE_CLR_EN_Enabled << GPIOTE_SUBSCRIBE_CLR_EN_Pos); NRF_GPIOTE20->CONFIG[5] = (GPIOTE_CONFIG_MODE_Task << GPIOTE_CONFIG_MODE_Pos)| (GPIOTE_CONFIG_OUTINIT_Low << GPIOTE_CONFIG_OUTINIT_Pos) | (2 << GPIOTE_CONFIG_PSEL_Pos) | (1 << GPIOTE_CONFIG_PORT_Pos); NRF_DPPIC20->CHENSET = (DPPIC_CHENSET_CH1_Enabled << DPPIC_CHENSET_CH1_Pos); NRF_DPPIC20->CHENSET = (DPPIC_CHENSET_CH2_Enabled << DPPIC_CHENSET_CH2_Pos); return 0; } SYS_INIT(enable_uart_de, EARLY, 20);

How to add RS‑485 DE pin control to console/shell UART on nRF52840?

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