LC60: What is the bus frequency after stop3 in FEE?

[BasePointer]

Hi,

My program works at Fbus = 6.291456 MHz in FEE mode (external crystal is 32768Hz)

I wonder the bus frequency after exiting stop3 mode. Will it work at SCM frequency or SCM / 2 for a while? And What would be SCM frequency at that state?

Note: Clock monitor is disabled.

10x,

BP.

[bigmac]

Hello BP,

When in SCM, the DCO frequency will be determined by the current setting for the filter bits.  On exit from Stop 3 mode, I might expect that the filter bits would remain unaltered from that which existed prior to entry to Stop 3.  If this is true, the DCO output frequency should be very close to its previous value, assuming that there has been no significant change to temperature or supply voltage.  Of course, if the device had previously been at an elevated temperature due to loading, it would cool during a lengthy Stop 3 period.

Regards,

Mac

[BasePointer]

Hi mac,

There is a training note about "Effects of STOP on ICG"

http://www.freescale.com/webapp/sps/site/training_information.jsp?code=WBT_28068&ftrnsrch=1#

Open the pdf, at page 9:

FEE mode
Startup is immediate at 1/2
pre-STOP frequency in
SCM until stabilization time
and then switch to external
reference

The LC60 datasheet doesn't contain any info about this.

Thank you,

BP.

[bigmac]

Hello BP,

I would suspect that the "half frequency" operation would be implemented by temporarily changing the RFD setting, rather than the DCO frequency, with the previous setting automatically restored once the external reference has stabilised and lock is regained.

I assume it is done this way to avoid any possibility that the maximum bus frequency be exceeded whilst in SCM mode.  It does seem strange that there is no mention in the datasheet.  I wonder if this applies only to a RFD setting of 1, or to all RFD settings.  If the latter, it is probably an extra divide by two stage that is switched into circuit.

Regards,

Mac