i.MX6DL BOOT_CFG pins pull up/down

[dismirli]

Hello,

We are designing a board with the i.MX6DL, and we want to use the BOOT_CFG pins to alter the boot flow during development. I want to avoid the external pullup/pulldown resistors in the BOOT_CFG pins as much as possible.

In the datasheet (IMX6SDLCEC.pdf), Table 98 ("Signals with Differing Before Reset and After Reset States") shows that the EIM pads have 100k pull-downs *before reset*. These pads are the BOOT_CFG signals. However, Table 97 (Out of reset condition) shows that many of these pads have 100k pull-ups *out of reset*.

Table 2-2 ("EIM recommendations for developer’s boot modes") of the Hardware Development Guide (IMX6DQ6SDLHDG.pdf) states that "If using GPIO override instead of fuses, the BOOT_CFG signals are required for proper functionality and operation and should not remain unconnected".

So the questions are:

- Why can't I leave the BOOT_CFG pins unconnected, if the datasheet shows that they have internal pull-up/down resistors?

- Can I assume that the default value of the BOOT_CFG signals is 0 (due to the 100k pull-downs), when the BOOT_CFG pins are sampled? That is to say, should I use Table 98 ("Before reset") or the ones of Table 97 ("Out of reset")?

Thank you,

Diego.

[igorpadykov]

Hi Diego

sampling point is described in p.13 spf-27452 i.MX6SL EVK schematic

Schematics (2)
Design files, including hardware schematics, Gerbers, and OrCAD files. (REV 1)
http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/i.mx-applications-process...

Also external resistors provide protection from noise.

Best regards
igor
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[dismirli]

Hi Igor, thanks for your answer.

However, something is still unclear:

From the spf-27452 document: "i.MX6SL reads values approximately 300uS to 1mS after reset released". From tables 97 and 98 in the datasheet (IMX6SDLCEC.pdf), the EIM_A16..24 signals (which map to BOOT_CFG3_0..7) have 100k pulldowns before reset, and are push-pull outputs after reset.

Of course, the BOOT_CFG sampling point can't be at the moment when EIM_A16..24 are outputs, but what is still unclear is:

- At the sampling point, what is the configuration of the internal pullups/pulldowns of the IMX6DL?

As a side note, I think that the 100k pulldowns/pullups are adequate in our case, despite the poor noise immunity, because the final product will be configured to boot from fuses. The pin boot selection will be used only for software development.

Thanks,

Diego.

[igorpadykov]

Hi Diego

exact sampling point and configuration of the internal pullups/pulldowns of the IMX6DL

is not specified, so recommended to use external pull resistors or use fuse boot option.

Best regards
igor

[dismirli]

Thanks Igor.

Diego.