Datasheet

78K0/Ix2 CHAPTER 5 CLOCK GENERATOR
R01UH0010EJ0500 Rev.5.00 155
Feb 28, 2012
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
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).
<1> X1 oscillator
This circuit oscillates a clock of fX = 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/PLL control register (RCM).
<3> External main system clock input
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.
<4> Multiplication function using PLL (phase locked loop)
If 4 MHz is selected for the main system clock, the PLL mode can be used. In this mode, a clock of ten times
the main system clock (40 MHz) can be supplied as the count clock of 16-bit timers X0 and X1, and a clock of
ten times the main system clock times 1/2 (20 MHz) can be supplied for all other clocks.
(2) Internal low-speed oscillation clock (clock for watchdog timer)
 Internal low-speed oscillator
This circuit oscillates a clock of f
IL = 30 kHz (TYP.). After a reset release, the internal low-speed oscillation clock
always starts operating.
Oscillation can be stopped by using the internal oscillation mode/PLL control register (RCM) when “internal low-
speed oscillator can be stopped by software” is set by option byte.
The internal low-speed oscillation clock cannot be used as the CPU clock. The following hardware operates with
the internal low-speed oscillation clock.
 Watchdog timer
 8-bit timer H1 (when f
IL, fIL/2
6
, or fIL/2
15
is selected)
Remark fx: X1 clock oscillation frequency
f
IH: Internal hi-speed oscillation clock frequency
f
EXCLK: External main system clock frequency
f
IL: Internal low-speed oscillation clock frequency