Clock Module
MCF52235 ColdFire® Integrated Microcontroller Reference Manual, Rev. 6
7-2
Freescale Semiconductor
7.3.2
External Clock Mode
In external clock mode, the PLL is bypassed, and the external clock is applied to EXTAL. The resulting
operating frequency is equal to the external clock frequency.
7.4
Low-power Mode Operation
This subsection describes the operation of the clock module in low-power and halted modes of operation.
Low-power modes are described in
Chapter 9, “Power Management.”
shows the clock module
operation in low-power modes.
Table 7-1. Clock Module Operation in Low-power Modes
In wait and doze modes, the system clocks to the peripherals are enabled and the clocks to the CPU and
memory are stopped. Each module can disable its clock locally at the module level.
In stop mode, all system clocks are disabled. There are several options for enabling or disabling the PLL
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.
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.
7.5
Block Diagram
shows a block diagram of the entire clock module. The PLL block in this diagram is expanded
in detail in
Low-power Mode
Clock Operation
Mode Exit
Wait
Clocks sent to peripheral modules only
Exit not caused by clock module, but normal
clocking resumes upon mode exit
Doze
Clocks sent to peripheral modules only
Exit not caused by clock module, but normal
clocking resumes upon mode exit
Stop
All system clocks disabled
Exit not caused by clock module, but clock
sources are re-enabled and normal
clocking resumes upon mode exit
Halted
Normal
Exit not caused by clock module
Because
of
an
order
from
the
United
States
International
Trade
Commission,
BGA-packaged
product
lines
and
part
numbers
indicated
here
currently
are
not
available
from
Freescale
for
import
or
sale
in
the
United
States
prior
to
September
2010:MCF52234CVM60,
MCF52235CVM60
