CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
101
<2> Setting the high-speed system clock as the main system clock (MCM register)
When XSEL and MCM0 are set to 1, the high-speed system clock is supplied as the main system clock
and peripheral hardware clock.
Selection of Main System Clock and Clock Supplied to Peripheral Hardware
XSEL MCM0
Main System Clock (f
XP
)
Peripheral Hardware Clock (f
PRS
)
1
1
High-speed system clock (f
XH
)
High-speed system clock (f
XH
)
Caution If the high-speed system clock is selected as the main system clock, a clock other than
the high-speed system clock cannot be set as the peripheral hardware clock.
<3> Setting the main system clock as the CPU clock and selecting the division ratio (PCC register)
When CSS is cleared to 0, the main system clock is supplied to the CPU. To select the CPU clock
division ratio, use PCC0, PCC1, and PCC2.
CSS
PCC2
PCC1
PCC0
CPU Clock (f
CPU
) Selection
0 0 0
f
XP
0 0 1
f
XP
/2 (default)
0 1 0
f
XP
/2
2
0 1 1
f
XP
/2
3
1 0 0
f
XP
/2
4
0
Other than above
Setting prohibited
(4) Example of setting procedure when stopping the high-speed system clock
The high-speed system clock can be stopped in the following two ways.
•
Executing the STOP instruction to set the STOP mode
•
Setting MSTOP to 1 and stopping the X1 oscillation (disabling clock input if the external clock is used)
(a) To execute a STOP instruction
<1> Setting to stop peripheral hardware
Stop peripheral hardware that cannot be used in the STOP mode (for peripheral hardware that
cannot be used in STOP mode, see
CHAPTER 14 STANDBY FUNCTION
).
<2> Setting the X1 clock oscillation stabilization time after standby release
When the CPU is operating on the X1 clock, set the value of the OSTS register before the STOP
instruction is executed.
<3> Executing the STOP instruction
When the STOP instruction is executed, the system is placed in the STOP mode and X1 oscillation
is stopped (the input of the external clock is disabled).
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