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Section 4 Clock Pulse Generators
4.1
Overview
Clock oscillator circuitry (CPG: clock pulse generator) is provided on-chip, including both a
system clock pulse generator and a subclock pulse generator. The system clock pulse generator
consists of a system clock oscillator and system clock dividers. The subclock pulse generator
consists of a subclock oscillator circuit and a subclock divider.
4.1.1
Block Diagram
Figure 4.1 shows a block diagram of the clock pulse generators.
System clock
oscillator
System clock
divider (1/2)
Subclock
oscillator
Subclock
divider
(1/2, 1/4, 1/8)
System clock
divider (1/8)
System clock pulse generator
Subclock pulse generator
Prescaler S
(13 bits)
Prescaler W
(5 bits)
OSC
OSC
1
2
X
X
1
2
ø
OSC
(f )
OSC
ø
W
(f )
W
ø /2
OSC
ø /2
W
ø /8
W
ø
SUB
ø/2
to
ø/8192
ø /2
W
ø /4
W
ø /8
to
ø /128
W
W
ø
ø /16
OSC
ø /4
W
øW
øOSC
Figure 4.1 Block Diagram of Clock Pulse Generators
4.1.2
System Clock and Subclock
The basic clock signals that drive the CPU and on-chip peripheral modules are ø and ø
SUB
. Four of
the clock signals have names: ø is the system clock, ø
SUB
is the subclock, ø
OSC
is the oscillator
clock, and ø
W
is the watch clock.
The clock signals available for use by peripheral modules are ø
OSC
, ø/2, ø/4, ø/8, ø/16, ø/32, ø/64,
ø/128, ø/256, ø/512, ø/1024, ø/2048, ø/4096, ø/8192, ø
W
, ø
W
/2, ø
W
/4, ø
W
/8, ø
W
/16, ø
W
/32, ø
W
/64,
and ø
W
/128. The clock requirements differ from one module to another.
4.2
System Clock Generator
Clock pulse can be supplied to the system clock divider either by connecting a crystal or ceramic
oscillator, or by providing external clock input.