Datasheet
78K0/Ix2 CHAPTER 5 CLOCK GENERATOR
R01UH0010EJ0500 Rev.5.00 175
Feb 28, 2012
<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 (fPRS)
1 1 High-speed system clock (fXH) High-speed system clock (fXH)
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 (fCPU) Selection
0 0 0 fXP
0 0 1 fXP/2 (default)
0 1 0 fXP/2
2
0 1 1 fXP/2
3
1 0 0 fXP/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 and stopping the X1 oscillation (disabling clock input if the external clock is used)
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, refer to CHAPTER 19 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).