Clock Module
MCF52110 ColdFire® Integrated Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
6-3
Preliminary
In stop mode, all system clocks are disabled. There are several options for enabling or disabling the PLL
or crystal oscillator in stop mode, compromising between stop mode current and wakeup recovery time.
The PLL can be disabled in stop mode, but requires a wakeup period before it can relock. The oscillator
can also be disabled during stop mode, but requires a wakeup period to restart.
When the PLL is enabled in stop mode (STPMD[1:0]), the external CLKOUT signal can support systems
using CLKOUT as the clock source.
There is also a fast wakeup option for quickly enabling the system clocks during stop recovery. This
eliminates the wakeup recovery time but at the risk of sending a potentially unstable clock to the system.
To prevent a non-locked PLL frequency overshoot when using the fast wakeup option, change the RFD
divisor to the current RFD value plus one before entering stop mode.
In external clock mode, there are no wakeup periods for oscillator startup or PLL lock.
6.5
Block Diagram
shows a block diagram of the entire clock module.
