Datasheet

78K0/Kx2-L CHAPTER 5 CLOCK GENERATOR
R01UH0028EJ0400 Rev.4.00 198
Sep 27, 2010
CHAPTER 5 CLOCK GENERATOR
5.1 Functions of Clock Generator
The clock generator generates the clock to be supplied to the CPU and peripheral hardware.
The following three kinds of system clocks and clock oscillators are selectable.
(1) Main system clock
<1> X1 oscillator
This circuit oscillates a clock of f
X = 1 to 10 MHz by connecting a resonator to X1 and X2.
Oscillation can be stopped by executing the STOP instruction or using the main OSC control register (MOC).
<2> Internal high-speed oscillator
This circuit oscillates a clock of f
IH = 4 MHz (TYP.)/8 MHz (TYP.). After a reset release, the CPU always
starts operating with this internal high-speed oscillation clock. Oscillation can be stopped by executing the
STOP instruction or using the internal oscillation mode register (RCM).
An external main system clock (f
EXCLK = 1 to 10 MHz) can also be supplied from the EXCLK/X2/P122 pin. An
external main system clock input can be disabled by executing the STOP instruction or using RCM.
As the main system clock, a high-speed system clock (X1 clock or external main system clock) or internal high-
speed oscillation clock can be selected by using the main clock mode register (MCM).
(2) Subsystem clock
Note
• Subsystem clock oscillator
This circuit oscillates at a frequency of f
XT = 32.768 kHz by connecting a 32.768 kHz resonator across XT1 and
XT2. Oscillation can be stopped by using the processor clock control register (PCC) and clock operation mode
select register (OSCCTL).
An external subsystem clock (f
EXCLKS = 32.768 kHz) can also be supplied from the EXCLKS/XT2/P124 pin. An
external subsystem clock input can be disabled by setting PCC and OSCCTL.
Note 78K0/KC2-L only
Remark f
X: X1 clock oscillation frequency
fIH: Internal high-speed oscillation clock frequency
f
EXCLK: External main system clock frequency
f
XT: XT1 clock oscillation frequency
f
EXCLKS: External subsystem clock frequency