Hello everyone,
I’m using the MIMXRT1042 XJM5B EVK and working with LPUART1. The LPUART1 pins are connected to the J1 (micro USB port). I’m able to successfully send and receive data on the terminal through the USB connection.
However, when I remove jumpers J11 and J13 (which connect the LPUART1 RX and TX lines to the USB interface) to use an external TTL-to-USB converter, I can receive data on the terminal only while debugging. Once I stop debugging and reset the board, the UART no longer echoes the data I send.
I observed the same behavior with LPUART4. I enabled the internal pull-up resistors (22 kΩ), but it still didn’t work. When I added external pull-ups on the RX and TX lines, the UART communication worked correctly, and I could see the echoed data on the terminal.
Has anyone else experienced this issue or can suggest why it only works during debugging?
Thank you for your reply.
I am using the "evkmimxrt1040_lpuart_edma_rb_transfer" SDK example on LPUART4, and I am seeing the same behavior on LPUART1 as well.
Thanks for your updated information.
1: Please use an oscilloscope to check the UART TX and RX signals to confirm whether the waveforms are normal. and also verify the UART baud rate ,please make sure there is no significant deviation.
2: When the issue occurs, please print the UART error logs , and check which LPUART error flags are set. please Kindly provide detailed information such as the specific error flags.
3: Which SDK demo are you using, and have you made any modifications to it?
Best Regards
Thank you for your reply,
My concern is that when I debug the LPUART4 code, the data on TX and RX works correctly even without an external pull-up. However, after exiting debug mode and flashing the code normally, the received and transmitted data becomes corrupted.
Hi @RajPadmani ,
Thank you so much for your interest in our products and for using our community.
Regarding your question, I check the schematic of MIMXRT1040-EVK,
In the architecture diagram of the NTS0102 (Figure 11), we can see a 10 kΩ resistor.
If the UART cable is long or there is significant external interference, it is recommended to add an external pull-up resistor on the RX line to ensure signal stability and avoid communication issues caused by a floating line.
Wish it helps you.
If you still have question about it, please kindly let me know.
Best Regards
MayLiu