topic Re: External 24MHz Clock For i.MX8QM in i.MX Processors

External 24MHz Clock For i.MX8QM

HWasti — Mon, 12 Feb 2024 12:02:03 GMT

Hello,

The i.MX8QM datasheet, in Section 4.1.4 states: " The system clock input requires a crystal using the internal oscillator amplifier."

Later in footnote 4 it states: "Fundamental frequency crystal with internal oscillator amplifier."

In numerous places in this section, the document explicitly mentions crystal and external clock for RTC_XTALI, but never for XTALI.

This implies that an external clock is not supported.

But later in Section 4.5.1 is titled "XTALI and RTC_XTALI (Clock Inputs) DC Parameters" implying that external clock input is supported for XTALI.

But in that section, it talks only about VIH and VIL for RTC_XTALI and is completely silent about high speed XTALI.

Questions:

1) For applications where the system will always be running and will never go into standby or shutdown modes, can an external 24MHz oscillator, connected to XTALI pin, be used?

2) What are the voltage levels for this external clock input?

Regards,

hwasti

Re: External 24MHz Clock For i.MX8QM

JorgeCas — Wed, 14 Feb 2024 16:14:15 GMT

Hello,

1) For applications where the system will always be running and will never go into standby or shutdown modes, can an external 24MHz oscillator, connected to XTALI pin, be used?

Yes, the chip has two XTAL modules, 24MHz XTAL and 32KHz XTAL modules (All of these modules needs to use an external clock source, you could use our MEK as reference, you can use a crystal or oscillator).

2) What are the voltage levels for this external clock input?

The 24 MHz oscillator can be driven with an external signal at the XTALI pin. The input voltage should never exceed the oscillator supply voltage (VDD_SCU_XTAL_1P8).

The 32 KHz oscillator can be driven with an external signal at the RTC_XTALI pin. The input voltage should never exceed the oscillator supply voltage (VDD_SNVS_LDO_1P8_CAP).

Here the specifications:

JorgeCas_1-1707927137994.png

The processor can also accept a 1.8 V logic level clock. The specification input voltages for are the next:

VIH between (0.5 X VDD +0.5v) and VDD

VIL between 0 and (0.5 VDD - 0.5v)

Best regards.

Re: External 24MHz Clock For i.MX8QM

HWasti — Wed, 14 Feb 2024 16:25:33 GMT

Hi Jorge,

Your initial reply was likely referencing a different chip. Thank you for correcting it so quickly.

Regards.

Re: External 24MHz Clock For i.MX8QM

JorgeCas — Wed, 14 Feb 2024 16:13:27 GMT

Answer corrected, I apologize for the confusion.

Best regards.