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

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

mbakker — Wed, 11 Mar 2026 07:56:35 GMT

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);

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

Avgerinos Bakalidis — Wed, 18 Feb 2026 08:48:15 GMT

Hello,

I tried your suggestion of using an RS-485 with auto direction capability and it worked.

More specifically I used the THVD1426DR (RS-485 Transceivers with Auto-direction Control) from Texas instruments and found out that the Zephyr shell is working as well as the MCUmgr on downloading a file with no issues, through the RS-485 half duplex connection.

Thank you Susheel Nuguru for your suggestion!

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

Susheel Nuguru — Mon, 02 Feb 2026 13:45:24 GMT

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.

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

Turbo J — Fri, 30 Jan 2026 16:20:46 GMT

You cant use UART shell directly here.

But there is also the dummy shell backend. Mcumgr subsystem uses that to tunnel shell commands over the mucmgr (smp) protocol - you may be able to do something roughly similar with your rs485 operations.