NEC 78K0 Series User Manual page 157

(2) Example of setting procedure when using internal high-speed oscillation clock as CPU clock, and
internal high-speed oscillation clock or high-speed system clock as peripheral hardware clock
<1> • Restarting oscillation of the internal high-speed oscillation clock
(See 6.6.2 (1) Example of setting procedure when restarting internal high-speed oscillation
clock).
• Oscillating the high-speed system clock
(This setting is required when using the high-speed system clock as the peripheral hardware clock.
See 6.6.1 (1) Example of setting procedure when oscillating the X1 clock and (2) Example of
setting procedure when using the external main system clock.)
Note The setting of <1> is not necessary when the internal high-speed oscillation clock or high-
speed system clock is already operating.
<2> Selecting the clock supplied as the main system clock and peripheral hardware clock (MCM register)
Set the main system clock and peripheral hardware clock using XSEL and MCM0.
XSEL MCM0
0
0
1
<3> Selecting the CPU clock 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
0
(3) Example of setting procedure when stopping the internal high-speed oscillation clock
The internal high-speed oscillation clock can be stopped in the following two ways.
• Executing the STOP instruction to set the STOP mode
• Setting RSTOP to 1 and stopping the internal high-speed oscillation clock
(a) To execute a STOP instruction
<1> Setting of 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 21 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
CHAPTER 6 CLOCK GENERATOR
Note
Selection of Main System Clock and Clock Supplied to Peripheral Hardware
Main System Clock (f
0 Internal high-speed oscillation clock
(f )
RH
1
0
PCC1 PCC0
0 0 0
0 0 1
0 1 0
0 1 1
1 0 0
Other than above
Preliminary User's Manual U17260EJ3V1UD
Note
) Peripheral Hardware Clock (f
XP
Internal high-speed oscillation clock
(f )
RH
High-speed system clock (f
CPU Clock (f ) Selection
CPU
f
XP
f /2 (default)
XP
2
f /2
XP
3
f /2
XP
4
f /2
XP
Setting prohibited
)
PRS
)
XH
157