The S32K148 MCU’s Low-Power UART (LPUART) peripheral can be used as the physical layer for Modbus RTU. Below is a concise walk-through of the minimal steps and a reference driver that receives variable-langth frames terminated by a newline character.

Physical-layer essentials

• Idle level: logic high (1)
• Start bit: logic low (0)
• Data bits: 8 (LSB first)
• Parity: even (typical for Modbus RTU)
• Stop bits: 1
• Baud rate: 115 200 bit/s in this example

Pin and clock setup

Route PTC7 (LPUART1_RX) and PTC6 (LPUART1_TX) in the Pins tool. The S32 SDK’s "expert mode" automatically enables the peripheral clock (PCC->PCCn[PCC_LPUART1_INDEX]), so no extra clock call is required.

Driver objects

static uint8_t  rxBuf[200];
static uint8_t  rxIdx;
static uint32_t rxLeft;

Initialisation

void LPUART1_Init(void)
{
    /* SDK-generated structures */
    LPUART_DRV_Init(INST_LPUART1, &lpuart1_State, &lpuart1_InitConfig0);

    /* Register non-blocking receive callback */
    LPUART_DRV_InstallRxCallback(INST_LPUART1, RxHandler, NULL);

    /* Kick off first byte */
    LPUART_DRV_ReceiveData(INST_LPUART1, rxBuf, 1);
}

Interrupt-driven callback

static void RxHandler(void *drv, uart_event_t evt, void *usr)
{
    (void)drv;
    (void)usr;

    status_t st = LPUART_DRV_GetReceiveStatus(INST_LPUART1, &rxLeft);

    if (st == STATUS_SUCCESS)          /* one byte received */
    {
        /* Append null terminator for string handling */
        rxBuf[rxIdx + 1] = 0;

        /* Reset index for next frame */
        rxIdx = 0;

        /* Re-arm for the next byte */
        LPUART_DRV_ReceiveData(INST_LPUART1, rxBuf, 1);
    }
    else if (evt == UART_EVENT_RX_FULL)
    {
        /* Buffer not yet full, keep collecting */
        if (rxBuf[rxIdx] != '\n' && rxIdx < sizeof(rxBuf) - 2)
        {
            ++rxIdx;
            LPUART_DRV_SetRxBuffer(INST_LPUART1, &rxBuf[rxIdx], 1);
        }
    }
}

With the peripheral now streaming bytes into rxBuf, higher-level Modbus RTU logic can parse the frame once the newline delimiter is detected.