
CHAPTER 6 CLOCK GENERATOR
User’s Manual U17473EJ2V0UD
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<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
fXP
0
1
fXP/2 (default)
0
1
0
fXP/2
2
0
1
fXP/2
3
1
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, see CHAPTER 22 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).
(b) To stop X1 oscillation (disabling external clock input) by setting MSTOP to 1
<1> Confirming the CPU clock status (PCC and MCM registers)
Confirm with CLS and MCS that the CPU is operating on a clock other than the high-speed system clock.
When CLS = 0 and MCS = 1, the high-speed system clock is supplied to the CPU, so change the
CPU clock to the subsystem clock or internal high-speed oscillation clock.
CLS
MCS
CPU Clock Status
0
Internal high-speed oscillation clock
0
1
High-speed system clock
1
×
Subsystem clock
<2> Stopping the high-speed system clock (MOC register)
When MSTOP is set to 1, X1 oscillation is stopped (the input of the external clock is disabled).
Caution
Be sure to confirm that MCS = 0 or CLS = 1 when setting MSTOP to 1. In addition, stop
peripheral hardware that is operating on the high-speed system clock.