topic Re: How to configure MPC5643L without using external crystal? in MPC5xxx

How to configure MPC5643L without using external crystal?

ningliu — Thu, 14 Sep 2017 18:44:22 GMT

I'm trying to configure MPC5643L by running with internal RC oscillator only. I'm currently running on a 16 MHz external crystal. The most likely way is to configure FMPLL0 and FMPLL1 to use internal RC oscillator. Right now, all clocks are driven by PLL0 and PLL1.

Please help me to do so.

Thanks!

Re: How to configure MPC5643L without using external crystal?

davidtosenovjan — Fri, 15 Sep 2017 13:09:22 GMT

Such configuration is possible by configuration of AUX Clock Selector, but internal RC oscillator is imprecise clock thus it is not being used too often.

Re: How to configure MPC5643L without using external crystal?

ningliu — Fri, 15 Sep 2017 13:21:13 GMT

That’s what I did by configuring:

1) CGM_AC3_SC register to select 16 MHz RC osc for PLL0

2) CGM_AC4_SC register to select 16 MHz RC osc for PLL1

However, the configuration was never successful. The program execution stuck at the while loop, waiting for PLL to lock.

By further reading MPC5643L user manual, chapter 27, Frequency-Modulated Phase-Locked Loop (FMPLL),

It never mentioned inter RC oscillator can be used as the colock source for PLL.

Do you have sample code I can try?

Thanks,

Ning

//////////////////////// The following are the code I used ////////////////////////////////////////////

/* Oscillator Output is Disabled as rootclock */

/* The End of Count Value for XOSC = 0x80 */

/* The XOSC Clock Interrupt: Disabled */

CGM.AC3_SC.B.SELCTL = 0; /* Select 16 MHz RC osc for PLL0 */

/* PLL0 reference clock source : 16MHz IRC */

CGM.AC4_SC.B.SELCTL = 0; /* Select 16 MHz RC osc for PLL1 */

/* PLL1 reference clock source : 16MHz IRC*/

CGM.FMPLL[0].CR.R = PLL_VALUE_0 | (0x01 << 8);

CGM.FMPLL[0].MR.R = 0x00000000;

/* The selected Spread Type: Down Spread */

/* The Modulation Period for FMPLL0: 0 */

/* Frequency modulation for PLL: Disabled */

/* The Increment Step for FMPLL0: 0 */

CGM.FMPLL[1].CR.R = PLL_VALUE_1 | (0x01 << 8);

CGM.FMPLL[1].MR.R = 0x00000000;

/* The selected Spread Type: Down Spread */

/* The Modulation Period for FMPLL1: 0 */

/* Frequency modulation for PLL: Disabled */

/* The Increment Step for FMPLL1: 0 */

Re: How to configure MPC5643L without using external crystal?

davidtosenovjan — Tue, 19 Sep 2017 09:21:57 GMT

I have tried it and it seems it is possible to run the whole system from IRC but XOSC still must run otherwise PLL does not stabilize. I am not sure why it is so. I am investigating.

Re: How to configure MPC5643L without using external crystal?

davidtosenovjan — Tue, 19 Sep 2017 09:53:09 GMT

Founded. The system cannot run without XOSC, otherwise PLL does not lock (even it is supposed to lock to IRC clock).

In this case I don't see any benefit to clock the system only by IRC clock as external oscillator must run anyway.

Re: How to configure MPC5643L without using external crystal?

ningliu — Tue, 19 Sep 2017 12:40:27 GMT

David,

Thanks! It’s Ok if the system is not stable. I’m doing this for MEI purpose. We have problem om EMI and hoping internal clock would reduce MEI issue.

Thanks,

Ning

Re: How to configure MPC5643L without using external crystal?

ningliu — Tue, 19 Sep 2017 13:06:51 GMT

David,

Thanks!

This agrees with my tests. Even I can configure PLL0/PLL1 using internal RC, the PLL does not lock.

I’ve made two versions of board:

1) a circuit has external crystal, but configured PLL0/PLL1 using internal crystal RC: it worked.

2) A circuit has external crystal removed, PLL can not lock.

Thanks for your kind help!

Ning