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ML674001 Series/ML675001 Series User’s Manual
Chapter 7
Power Management
7-11
7.3.5
Stopping Clock Signals to Functional Blocks
This LSI provides software control over the clock signals to individual functional blocks.
The following Table lists the functional blocks with clock signal control.
Block
In software
With DRAME_N
pins
Notes
SIO
O
TIC
O
UART
O
SSIO
O
I2C
O
DMAC
O
Do not stop the clock signal while a DMA transfer is
in progress.
DRAMC
O
Always switch DRAM to self refresh operation before
stopping the clock signal in software.
TIMER
O
(each timer
individually)
Stopping the clock signal suspends the counter. If
the timer is operational, restoring the clock signal
causes counting to resume with that counter value.
PWM
O
Stopping the clock signal suspends the counter. If
the PWM block is operational, restoring the clock
signal causes counting to resume with that counter
value.
A/D
O
Stop conversion before stopping the clock signal.
Do not access a functional block while its clock signal is stopped. Accessing the DMA controller or DRAM
controller triggers an abort exception. Accessing other functional blocks risks unreliable operation.
If the clock signal to a functional block is stopped, shifting to HALT or STANDBY mode and back again
restarts the clock signal only if the wake-up signal is a reset.
7.3.6
Clock Gear
Modifying the CCLK or HCLK divisor in the clock gear control (CGBCNT0) register dynamically changes
the corresponding clock frequency to 1/1, 1/2, 1/4, 1/8, 1/16, or 1/32* times the base frequency.
Changing the CCLK frequency with the clock gear affects the system timer, serial I/O (SIO) block,
watchdog timer (WDT), timers, PWM block, UART, and DRAM refresh clock; changing the HCLK
frequency does not.
If the clock gear is producing lower clock frequencies, shifting to HALT or STANDBY mode and back
again restores the 1/1 settings only if the wake-up signal is a reset.
Always switch DRAM to self refresh operation before reducing the clock signal frequency below the
minimum specified for reliable operation.
[Notes]
*1: 1/32 M675001 Series only
Notes for each function in using Clock Gear
SIO: When changing the CCLK, the communication through SIO should be stopped.
UART: When changing the CCLK, the communication through UART should be stopped.
WDT: The WDT interval will be changed when CCLK Clock Gear is changed.
DRAM: Refresh cycle setting should be set based on final CCLK frequency, before changing clock.
If refresh cycle is changed dynamically, must be set CCLK = 1/1 of clock gear temporally.
PWM: The PWM frequency is changed when the CCLK clock frequency is changed.
AD converter: The AD conversion should be stopped when changing CCLK clock frequency.