Why is a SN74LVC1G06 connected between emmc and AM3359 on Beaglebone black?

As the topic shown,I’m wondering if it’s necessary to use a SN74LVC1G06 between emmc and AM3359.
Is the SN74LVC1G06 used for voltage level matching?But both the AM3359’s GPIO and emmc’s RSTn pin can be drivern by 3.3V.
Or the SN74LVC1G06 is used as a inverter,but why?

To insure that on power up, the eMMC is not held reset which would result in you not being able to boot from the eMMC because it was in reset. The purpose of the device is to invert the polarity of the default state of the processor pin. If you look at the datasheet for the processor, you will see that the default state of the pin is low on power up.


Thanks for your reply.
Could you show me the specific page of AM3359’s datasheet where describes the default state of the pin?I have read the datasheet,but found nothing.
I’m new here and appreciate your kind help.

在 2014年3月25日星期二UTC+8下午9时00分26秒,Gerald写道:

Section 2.2 starting on page 16 lists the Ball (pin) Characteristics of
the AM335x, including available pin multiplexing modes, reset states,
driver strength, availability of pull-up/down resistors, etc.

This design might have NO effect!

Where is the pin’s default state, just like Gerald says ‘you will see that the default state of the pin is low on power up’?

在 2014年3月26日星期三UTC+8下午7时11分54秒,Charles Steinkuehler写道:

Table 2-7. Multiple pages.


Ball R14 on the ZCZ is on page 22. Both the ball reset state (power-on
reset) and reset rel state (reset signal asserted) are "L", which the
start of section 2.2 tells you is "High-impedance with an active
pulldown resistor".

Get it!
Thank Charles and Gerald for patiently answering my questions.
And is there anyone who could kindly verify c2h2’s question ‘Does this mean this design doesn’t affect anything, unless we change ECSD
register byte 162, bits[1:0] to 0x1’?

在 2014年3月26日星期三UTC+8下午9时46分54秒,Charles Steinkuehler写道:

That is correct. I made the assumption that someone would do that. Without this in there, the board would never boot from eMMC.


Note that this setting in the eMMC is write-once, so if it ever gets
setup for hardware reset (and it should from the factory IMHO since the
'Black is supposed to support disabling the eMMC via the cape manager),
it will be in effect from then on (including after power-on reset) and
there is no way to reverse the process.

So _something_ needs to be done to insure the eMMC is not in reset at
boot. I expect Gerald has reasons for using the pin he did along with
the inverter instead of other options (pull-up resistor, choosing a pin
with a pull-up instead of pull-down, etc).

The reason I used that pin was that it was not being used for anything else. Remember. We were trying to maintain compatibility with the BeagleBone.

As to enabling that bit at the factory, that is up to the SW people to decide. We use the SW that ships with the boards that comes from the community.