i.MX8M - Nano external oscillator

[JHT]

Hello,

I believe that I have read the relevant previous posts regarding using an external clock for the 24MHz ref input. 

https://community.nxp.com/t5/i-MX-Processors/external-oscillators-for-i-MX8M/m-p/789124#M122307

Our plan is to attach the osc output from an external clk to B27 on the Nano and divide down the voltage to to somewhere between 1V3 and 0V3. 

We think we know, but are not 100% certain, where in the sequence is the 24MHz is expected. If someone could validate our suppositions that would be most helpful.

It looks to us like the 24MHz clock come on at time slot 7 as per the 8MNANOD4-EVK (seen in the power tree below ) or timeslot 8 from the datasheet.   It looks like the 24MHz clock does not need to be stable at timeslot 7 as it is being turned on - correct?

Thanks JT

[Rita_Wang]

1. Use 24MHz OSC with 1.8V IO

24MHz circuit's power is VDD_24M_XTAL_1P8, So the level of 24MHz OSC should be 1.8V

2. OSC's output is connected to CPU 24M_XTALI PIN

3. Connect 22pF capacitor on CPU 24M_XTALO PIN

[JHT]

Thank you very much for the reply,

 It really helps. We thought 1V8 but wasn't sure given what was on the forum. The main question remains.

Is there a critical time in the power_on sequence when the external osc needs to be on and stabilized or is it as simple as before PoR_B is deasserted?

Best - JT