Use IOMUXC_SetPinMux() function to switch between lpuart and gpio,sometimes serial start bit miss.

[FanXH]

GPIO_init();
LPUART2_init();
while(1)
{
    IOMUXC_SetPinMux(IOMUXC_GPIO_AD_B1_02_GPIO1_IO18, 0U);
    GPIO_WritePinOutput(GPIO1, 18U, 0);
    use_tmr_delay1ms();
    GPIO_WritePinOutput(GPIO1, 18U, 1);
    IOMUXC_SetPinMux(IOMUXC_GPIO_AD_B1_02_LPUART2_TX, 0U); 
    LPUART_Send(0x55);
}

Sometimes it's normal like this:

normal

But sometimes it's not normal,it should have some high level before start bit

error

[Omar_Anguiano]

Hello
Hope you are well.

It is important to add the pin configuration when you change between LPUART and GPIO.
The time that pin stays in high from GPIO_Write to LPUART_Send is variable, if you want to keep it consistent I suggest you add a small delay between.

If you have more questions do not hesitate to ask me.
Best regards,
Omar