Preliminary User’s Manual U19014EJ1V0UD
81
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 kinds of system clocks and clock oscillators are selectable.
(1) Main system clock
<1> X1 oscillator
This circuit oscillates a clock of f
X
= 12 or 16 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
RH
= 16 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
= 12 or 16 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 MOC.
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) Internal low-speed oscillation clock (clock for watchdog timer)
•
Internal low-speed oscillator
This circuit oscillates a clock of f
RL
= 240 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 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
RL
, f
RL
/2
7
, or f
RL
/2
9
is selected)
Remarks 1.
f
X
:
X1 clock oscillation frequency
2.
f
RH
:
Internal high-speed oscillation clock frequency
3.
f
EXCLK
:
External main system clock frequency
4.
f
RL
:
Internal low-speed oscillation clock frequency
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