i.MX RT1060 Serial Internal Boot Mode with LPUART1 Connected to USB-Serial Cable

[MulattoKid]

Hi,

I'm experiencing a strange issue on a RT1060 where if I have the boot pins configured as internal boot and have a USB-Serial cable connected to LPUART1 (which is used when in Serial Downloader mode) the MCU seems to crash. It doesn't boot the FW and doesn't enter Serial Downloader mode (Secure Provisioning Tool is unable to connect).

I've narrowed it down to the LPUART1_RXD (GPIO_AD_B0_13) being connected. Without it being connected the MCU boots fine. It also seems to persist between resets. I.e. if I power on the MCU with LPUART1_RXD connected to the USB-Serial cable it doesn't boot, and if I disconnect LPUART1_RXD and reset the MCU it still doesn't work, but if I power cycle after disconnecting LPUART1_RXD it works.

Any ideas what could cause this? Does the boot ROM read the state of LPUART1_RXD even in internal boot mode (but a reset should re-trigger any logic related to that, right)?

Thanks,
Daniel

[Omar_Anguiano · Accepted solution]

Hello, hope you are well.

It is not suggested having signal applied to the pins before powering up the MCU, this may lead to issues like booting.
First, the ROM code polls the UART1 signals from TXD1/RXD1. Add a 10-kΩ pull up resistor to the TXD1/RXD1 pins to avoid an invalid trigger of the UART port.

Best regards,
Omar

[MulattoKid]

Hi @Omar_Anguiano,

Thank you for the information!