iMX 91 FRDM UART3 Connection

sivakami — Fri, 09 Jan 2026 10:35:30 GMT

hi,

i am using FRDM-imx91, i need to enable UART3 in P11 Connector. i can use that Pin 8 and 9 as GPIO.

root@imx91frdm:~# gpioset --chip gpiochip0 14=0
^C
root@imx91frdm:~# gpioset --chip gpiochip0 14=1
^C
root@imx91frdm:~# gpioset --chip gpiochip0 14=0
^C
root@imx91frdm:~# gpioinfo | grep 14
line 14: unnamed output
line 14: unnamed input
line 14: unnamed input
line 14: unnamed input
line 14: unnamed output consumer=regulator-vdd-12v
root@imx91frdm:~# gpioinfo | grep 15
line 15: unnamed input
line 15: unnamed input
line 15: unnamed input
line 15: unnamed input
line 15: unnamed output
root@imx91frdm:~# killall gpioset
gpioset: no process found
root@imx91frdm:~# gpioinfo | grep 14
line 14: unnamed output
line 14: unnamed input
line 14: unnamed input
line 14: unnamed input
line 14: unnamed output consumer=regulator-vdd-12v
root@imx91frdm:~#
but i couldnot use as UART, i have see as below ttyLP*
root@imx91frdm:~# dmesg | grep ttyLP
[ 0.000000] Kernel command line: console=ttyLP0,115200 earlycon root=/dev/mmcblk0p2 rootwait rw
[ 0.820223] 44380000.serial: ttyLP0 at MMIO 0x44380010 (irq = 17, base_baud = 1500000) is a FSL_LPUART
[ 0.829548] printk: console [ttyLP0] enabled
[ 0.853209] 425a0000.serial: ttyLP5 at MMIO 0x425a0010 (irq = 18, base_baud = 1500000) is a FSL_LPUART
[ 1.918196] 42590000.serial: ttyLP4 at MMIO 0x42590010 (irq = 107, base_baud = 1500000) is a FSL_LPUART
root@imx91frdm:~#

How to send data in UART?

Re: iMX 91 FRDM UART3 Connection

Chavira — Fri, 09 Jan 2026 15:39:46 GMT

Hi @sivakami,

Thank you for contacting NXP Support.

UART3 is not enabled by default on this platform. To enable it, you must modify the original device tree to include the UART3 node.

I have attached a modified device tree that enables UART3 for the FRDM board.
Please follow the procedure below to compile and flash the updated device tree, after which UART3 will be available for use.

If you have any questions or need further assistance, please let us know.

How to compile Linux Kernel Image and device tree using Yocto SDK

Best regards,
Chavira

topic Re: iMX 91 FRDM UART3 Connection in i.MX Processors

iMX 91 FRDM UART3 Connection

Re: iMX 91 FRDM UART3 Connection