Switching boot mode without cycling power

[adevries]

Hello Community,

If I wish to change the boot mode / boot configuration  of the 8M Mini, is it necessary to power the processor down completely before doing so? Or is it acceptable to simply assert signal POR_B, change the BOOT_MODE and BOOT_CFG pins, and then de-assert signal POR_B?

Also, is it necessary for BOOT_MODE, TEST_MODE, and other boot configuration inputs to be pulled high or low through a resistor? Or can the inputs be tied directly to NVCC_JTAG or GND?

Thanks

[igorpadykov · Accepted solution]

Hi adevries

yes in general it is sufficient to assert signal POR_B for changing processor boot mode / boot configuration.

>is it necessary for BOOT_MODE, TEST_MODE, and other boot configuration inputs

>to be pulled high or low through a resistor? Or can the inputs be tied directly to NVCC_JTAG or GND?

recommended to use resistors as before processor is fully powered-up, internal logic controlling

the input connection circuits is not initiated, so there may be leakage through boot configuration inputs.

Best regards
igor

[adevries]

Hi Igor,

I know the recommendation is to normally use resistors, but I've got an application where I'm looking to temporarily override what the pin is pulled to. For example, if I normally have BOOT_MODE1 set to 0 by pulling it down to GND through a 100k resistor, I'm looking to temporarily set it to 1 by connecting the pin to NVCC_JTAG.

recommended to use resistors as before processor is fully powered-up, internal logic controlling

the input connection circuits is not initiated, so there may be leakage through boot configuration inputs.

Will the leakage through the pins be limited to the leakage parameters listed in Table 20 and 21 of the i.MX 8M Mini Datasheet? 

[igorpadykov]

Hi adevries

>Will the leakage through the pins be limited to the leakage parameters

>listed in Table 20 and 21 of the i.MX 8M Mini Datasheet?

not. Unfortunately they are not specified.

Best regards
igor

[adevries]

Hi Igor,

That is very good to know. Since there must be a resistor to control the leakage, current, could you recommend what value resistor I should use?

In the image below, I have BOOT_MODE1 pulled high to NVCC_JTAG with a 4.7k resistor. I'm looking to temporarily override that and pull it low with a stronger resistor. What value would you recommend?

Thanks

[igorpadykov]

Hi adevries

general recommendation is to follow nxp i.MX8MMini reference schematic

i.MX 8M Mini Evaluation Kit LPDDR4 Design Files

and

i.MX 8M Mini Hardware Developer’s Guide

p.14 SPF-31407 BaseBoard schematic gives similar example for overriding boot resistors.

Best regards
igor

[adevries]

Hi Igor,

Okay, thanks for the recommendation. I'll adjust my design to more closely follow the baseboard schematic.

Thanks