BT_CFG pins pulldowns necessary on RT1052?

[joshelijah]

I’m using the RT1052 in a system that will boot from QSPI NOR flash or a serial downloader.

(For reference, here are the design files i.MX RT1050 Evaluation Kit|NXP )

My intention is to breakout the following BT_CFG pins to a header so that I can configure the boot.

BT_CFG[11]

BT_CFG[8]

BT_CFG[3]

BT_CFG[2]

BT_CFG[1]

I want the remaining BT_CFG pins to be at logic 0.

My question is, do I need to pull them down externally?

Page 9, table 9 in the doc below suggests that I must not leave them floating

https://www.nxp.com/docs/en/user-guide/MIMXRT1050HDUG.pdf

But I also read that they are, by default, they are pulled low on reset (see page 75, table 70)…

https://www.nxp.com/docs/en/data-sheet/IMXRT1050CEC.pdf

So which one is it, can I leave these pins unconnected and rely on the internal pulldowns, or do I need to connect them to ground externally?

Thanks in advance.

[joshelijah]

Hi Igor,

Thanks for the response!

Some of the boot_cfg pins I can set permanently to ground in my application.

Would it be acceptable to ties these boot_cfg together and connect to a single pulldown resistor to ground, or does each boot_cfg need its own pulldown resistor?

[igorpadykov · Accepted solution]

Hi Josh

yes one can use single pulldown resistor to ground.

Best regards
igor

[alvaro_pinto]

Hi Igor,

If the fuses have been program correctly and the unit boot from fuses mode, is it safe to remove all the pull-down resistors? 

[igorpadykov]

Hi Josh

recommended to follow Hardware Guide and use external resistors

to avoid noise and uncertainty of signal state on boot pins as reset process

is complex algorithm described in sect.51.6.1.2 Reset Handling MXRT1050 Reference Manual

Best regards
igor
-----------------------------------------------------------------------------------------------------------------------
Note: If this post answers your question, please click the Correct Answer button. Thank you!
-----------------------------------------------------------------------------------------------------------------------