Inquiries about the reference clock setting of the MPC5777C.

[youngseolee]

Dear NXP support team.

I have a question about the reference clock setting of MPC5777C.

My development board using previous generation devices used the external oscillator output as a reference clock by setting PLLCFG[0:1].

However, for MPC5777C, PLLCFG [0:1] does not affect the reference clock setting, and it seems that the reference clock is set using DCF.

To load DCF, MPC5777C needs to boot, but my development board only has the output of the external oscillator connected to EXTAL pin, and XTAL pin has no signal connected.

Even if I design like this, can I boot MPC5777C and load DCF?

[davidtosenovjan]

DCF records are loaded during startup. Initially MCU boots with internal RC, so I don’t see any issue anyway.

[youngseolee]

Thank you for your reply.

I have one more question.

Can the MPC5777C be connected to a debugger such as Power Debugger(Trace32) while initially operating using internal RC?

[rweiss]

You may need to set a lower debug frequency, so that it does not exceed 1/4th of the core frequency. 3 MHz should be sufficiently low:

SYStem.CPU MPC5777C
SYStem.BdmClock 3.MHz
SYStem.Up

[davidtosenovjan]

Yes, definitely. The device is clocked by RC until it is manually switched to other source by startup code.