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Activating the XTAL output on K61 chip

Question asked by Jim Clay on Dec 27, 2012
Latest reply on Jan 3, 2013 by Jim Clay

We have built a custom board that has a MK61FN1M0CAA12 chip.  We want to use the OSC0 external crystal as the reference for the system clocks, but we cannot get the chip to activate the crystal, and by activate I mean put a DC voltage on the XTAL0 pin.  Without the DC voltage the crystal does not, of course, oscillate.  I have rechecked the layout and actual hardware and everything looks correct as far as I can tell.

 

We have done the following:

1) Verify that PORTA_PCR18 and PORTA_PCR19 (the pins that XTAL0 and EXTAL0 use) are 0.

2) Write 0xA2 to OSC_CR (enable the oscillator, introduce an 8 pF load).

3) Write 0x1C to MCG_C2 (crystal, high-gain, high frequency range)

4) Write 0xA0 to MCG_C1 (selects external reference as system clock source, sets FRDIV such that clock is in right range, enables oscillator)

 

I am doing all of these things from CodeWarrior using the Multilink Universal debugger.  I assume that the chip's clocking state machine can transition in this scenario.

 

The one clear mistake that we have made is to pick a 20 MHz crystal oscillator, which can't be divided down to 32 kHz.  We will replace it with a 16 MHz crystal, or some other appropriate frequency.  But seeing as how the crystal isn't even oscillating yet, I don't think that that is the problem at this point.

 

Any help would be greatly appreciated.

 

EDIT: I forgot to mention that the MCG_S[OSCINIT0] value never goes to 1, which is expected since the crystal never oscillates.

 

Message was edited by: Jim Clay

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