Using crystal instead of clock generator with K60F120M

[ARQuattr]

I have a custom board based on the K60F120M tower board, which has an clock generator on XTAL0/EXTAL0, and a crystal on XTAL1/EXTAL1.  I left off the external clock, and have only the crystal, but unfortunately I left it on XTAL1/EXTAL1, and now it seems like that won't work.

But when I change to use XTAL0/EXTAL0, the basic tower board demo projects don't run anyway.

1. Is it possible to run the device off a crystal on XTAL1/EXTAL1 pins only?  From reviewing the reference manual, it looks like XTAL1/EXTAL1 can only drive some peripherals, and not all internal clocks.  Is this right?

2. Assuming I move the crystal to the XTAL0/EXTAL0 pins, is there some clock configuration change I need to make to work off the crystal as opposed to a clock input?  I noticed some settings such as gain, etc., but I tried various things and couldn't get it starting.  It stalls in __pe_initialize_hardware of bsp_cm.c in a while loop waiting for a required clock condition.

Thanks

[Kan_Li]

Hi Angelo,

Yes, it is possible to run the device off a crystal on XTAL1/EXTAL1 pins only, MCGPLL1CLK is one of the alternative clock sources for MCGOUTCLK, so it can be used to drive all the on-chip peripherals. and if you move the crystal to XTAL0/EXTAL0 pins， there should be changes in the code for original reference clock configuration, you may refer to the demos in C:\Freescale\CW MCU v10.6\MCU\CodeWarrior_Examples\Processor_Expert\Kinetis\TWR-K40X256 for details, since TWR-K40X256 uses a 8MHz crystal connected with XTAL/EXTAL pins.

Hope that helps,

Have a great day,
Kan

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[ARQuattr]

Thank you Kan,

     I couldn't find that folder in CW10.5 so I'll install 10.6 and check again.  In the meantime I tried to create a new PE project to let it generate code for my configuration and see what it looks like, but I wasn't too sure about how it should be configured since there are so many options.  Going through the manual is somewhat helping but again there is a lot going on and I'm not familiar enough with the entire clock tree to know what options to use, e.g. FEI, FEE, PBE, etc.

     If I leave the crystal on the same XTAL1/ETXAL1 pins I have it on now, what registers should I be looking at to change it from external clock to crystal?

Thanks,

Angelo

[Kan_Li]

Hi Angelo,

According to my experience on PE, I think you may configure the clock source from ref clock to crystal by the following steps:

1. change system oscillator:

2.change MCG mode and PLLx

3.Set PLL output freq:

4.Set system clocks:

Hope that helps,

Have a great day,
Kan

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[ARQuattr]

Thank you Kan,

     It looks like you have it set to use XTAL0.  If I try to set it up using XTAL1, I'm not able to select oscillator 1 for the MCG reference clock.  Please see the attached image.

     Using the demo project for the K60 tower board, on my custom board that has a 12MHz crystal on XTAL1, and nothing on XTAL0, the crystal oscillates but the device doesn't run.  I tried to redirect the clock to MCG (as shown in the image, and also changing MCG control registers directly), but I can't get it to run.

     If I rewire the crystal to XTAL0, it doesn't oscillate.  I enabled the PORTA_PCR19 MUX (since it was getting a reference clock on one pin only and not a crystal connection on the tower), and I enabled the oscillator (EREFS0=1 in MCG_C2), but I still don't get the crystal oscillating.

     I'm not sure what to try next.

Thanks,

Angelo

[Kan_Li · Accepted solution]

Hi Angelo,

The RTC oscillator is needed for such case, that might add a little bit cost for a 32.768KHz crystal, but you may configure the clock as below:

I have also successfully implemented it based on TWR-K70, you may try it as well on TWR-K60F120M.

Hope that helps,

Have a great day,
Kan

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[ARQuattr]

Thanks Kan,

     Do you know if this would mean that I still need an oscillator on XTAL1?  I.e. the PLL reference select options are OSC0 or OSC1, so I assume I can't just run everything off the RTC crystal only, correct?

Thanks,

Angelo

[Kan_Li]

Hi Angelo,

Yes, the crystal on XTAL1 is still needed , with a RTC crystal on the RTC oscillator you may use PLL1 in PEE mode, and generate system clock, bus clock , DDR2 clock for associated modules.

Have a great day,
Kan

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