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i.MX6DL BOOT_CFG pins pull up/down

Question asked by Diego Ismirlian on Nov 23, 2017
Latest reply on Nov 29, 2017 by Diego Ismirlian



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,