Datasheet

78K0/Ix2 CHAPTER 5 CLOCK GENERATOR
R01UH0010EJ0500 Rev.5.00 174
Feb 28, 2012
(1) Example of setting procedure when oscillating the X1 clock
<1> Setting P121/X1 and P122/X2/EXCLK pins and selecting X1 clock or external clock (OSCCTL register)
When EXCLK is cleared to 0 and OSCSEL is set to 1, the mode is switched from port mode to X1 oscillation
mode.
EXCLK OSCSEL Operation Mode of High-
Speed System Clock Pin
P121/X1 Pin P122/X2/EXCLK Pin
0 1 X1 oscillation mode Crystal/ceramic resonator connection
<2> Controlling oscillation of X1 clock (MOC register)
If MSTOP is cleared to 0, the X1 oscillator starts oscillating.
<3> Waiting for the stabilization of the oscillation of X1 clock
Check the OSTC register and wait for the necessary time.
During the wait time, other software processing can be executed with the internal high-speed oscillation clock.
Cautions 1. Do not change the value of EXCLK and OSCSEL while the X1 clock is operating.
2. Set the X1 clock after the supply voltage has reached the operable voltage of the clock to be
used (refer to CHAPTER 28 ELECTRICAL SPECIFICATIONS).
(2) Example of setting procedure when using the external main system clock
<1> Setting P121/X1 and P122/X2/EXCLK pins and selecting operation mode (OSCCTL register)
When EXCLK and OSCSEL are set to 1, the mode is switched from port mode to external clock input mode.
EXCLK OSCSEL Operation Mode of High-
Speed System Clock Pin
P121/X1 Pin P122/X2/EXCLK Pin
1 1 External clock input mode Input port External clock input
<2> Controlling external main system clock input (MOC register)
When MSTOP is cleared to 0, the input of the external main system clock is enabled.
Cautions 1. Do not change the value of EXCLK and OSCSEL while the external main system clock is
operating.
2. Set the external main system clock after the supply voltage has reached the operable voltage
of the clock to be used (refer to CHAPTER 28 ELECTRICAL SPECIFICATIONS).
(3) Example of setting procedure when using high-speed system clock as CPU clock and peripheral hardware
clock
<1> Setting high-speed system clock oscillation
Note
(Refer to 5.6.1 (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 high-speed system clock is already operating.