HCS12X - MCU Stop mode

[Ajay2006]

Hi,

I would like to get one information reg. the below:

 In S12X, is it possible to enable PLL lock interrupt & enter the low power modes like WAIT, Pseudo Stop & Full Stop Modes? 

From what we are seeing, if the PLL lock interrupt is enabled, then we are not able to enter the Full stop mode. Is it a basic micro behavior? What about the other 2 modes? 

If anyone can help, please reply.

Thanks in Advance.

Regards,

 -Aj

[Steve]

I need to double check but I believe what is happening is: you are executing the STOP instruction, the clock is stopping, the PLL is (as expected) losing lock, and the resulting interrupt is waking the part up again. In this case the solution would be to disable the PLL interrupt before executing STOP.

When entering WAIT mode you have the choice of deselecting the PLL automatically if required - see the PLLWAI bit for more info. Although, in that mode it may be useful to know if the PLL loses lock.

You need to be careful when entering STOP (or Pseudo-STOP or WAIT) that all of the possible routes to waking you up again are not pending otherwise you will bounce right back again.

[Ajay2006]

Thanks.

Does this mean that:

If LOCKIE bit is set and stop instruction is executed, MCU enters stop mode.

But eventually PLL loses clock and sets PLL Lock Interrupt flag which brings CPU out of stop mode.

Can I conclude with this that LOCKIE cannot be enabled to ensure MCU stalls ( Clock stops)?

Regards,

    -Aj

[Steve]

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Ajay2006 wrote:

Can I conclude with this that LOCKIE cannot be enabled to ensure MCU stalls ( Clock stops)?

---

I can confirm that if the LOCKIE is set when the CPU enters stop then the LOCK interrupt will cause the CPU to immediately restart (if the interrupt is going to the CPU and if the PLL was in lock before the STOP instruction). The simplest solution is probably to set LOCKIE to 0.

There are all sorts of alternative scenarios if you have XGATE handling the LOCK interrupt but unless you need the extra flexibility I'd stick with the disable LOCK interrupt option.

[Alban]

Hello,

The PLL does not work in full stop mode. There is no clock/oscillator in full stop mode.

Wait does have the clock full on.

Alban