CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
99
5.6 Controlling Clock
5.6.1 Controlling high-speed system clock
The following two types of high-speed system clocks are available.
•
X1 clock:
Crystal/ceramic resonator is connected across the X1 pin.
•
External main system clock: External clock is input to the EXCLK pin.
When the high-speed system clock is not used, the X1/P121 and X2/EXCLK/P122 pins can be used as I/O port
pins.
Caution The X1/P121 and X2/EXCLK/P122 pins are in the I/O port mode after a reset release.
The following describes examples of setting procedures for the following cases.
(1) When oscillating X1 clock
(2) When using external main system clock
(3) When using high-speed system clock as CPU clock and peripheral hardware clock
(4) When stopping high-speed system clock
(1) Example of setting procedure when oscillating the X1 clock
<1> Setting frequency (OSCCTL register)
Using AMPH, set the gain of the on-chip oscillator according to the frequency to be used.
AMPH
Note
Operating Frequency Control
0 f
XH
≤
10 MHz
1
10 MHz < f
XH
Note
Set AMPH before setting the peripheral functions after a reset release. The value of AMPH can
be changed only once after a reset release. When AMPH is set to 1, the clock supply to the CPU
is stopped for 5
µ
s (MIN.).
Remark
f
XH
: High-speed system clock oscillation frequency
<2> 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
<3> Controlling oscillation of X1 clock (MOC register)
If MSTOP is cleared to 0, the X1 oscillator starts oscillating.
electronic components distributor
