19
Clock Generating Circuit
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Clock Generating Circuit
The clock generating circuit contains two oscillator circuits that supply the operating clock sources to the
CPU and internal peripheral units.
Table 2. Main clock and sub clock generating circuits
Main clock generating circuit
CPU’s operating clock source
Internal peripheral units’
operating clock source
Ceramic or crystal oscillator
X
IN
, X
OUT
Available
Oscillating
Externally derived clock can be input
Sub clock generating circuit
CPU’s operating clock source
Timer A/B’s count clock
source
Crystal oscillator
X
CIN
, X
COUT
Available
Stopped
Use of clock
Usable oscillator
Pins to connect oscillator
Oscillation stop/restart function
Oscillator status immediately after rese
t
Other
Example of oscillator circuit
Figure 15 shows some examples of the main clock circuit, one using an oscillator connected to the circuit,
and the other one using an externally derived clock for input. Figure 16 shows some examples of sub clock
circuits, one using an oscillator connected to the circuit, and the other one using an externally derived clock
for input. Circuit constants in Figures 15 and 16 vary with each oscillator used. Use the values recom-
mended by the manufacturer of your oscillator.
Microcomputer
(Built-in feedback resistor)
X
IN
X
OUT
Open
Externally derived clock
Vcc
Vss
Microcomputer
(Built-in feedback resistor)
X
IN
X
OUT
R
d
C
IN
C
OUT
(Note)
Note: Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive
capacity setting. Use the value recommended by the maker of the oscillator.
When the oscillation drive capacity is set to low, check that oscillation is stable. Also, if the oscillator manufacturer's
data sheet specifies that a feedback resistor be added external to the chip, insert a feedback resistor between X
IN
and X
OUT
following the instruction.
Microcomputer
(Built-in feedback resistor)
X
CIN
X
COUT
Open
Externally derived clock
Vcc
Vss
Note: Insert a damping resistor if required. The resistance will vary depending on the oscillator and the oscillation drive
capacity setting. Use the value recommended by the maker of the oscillator.
When the oscillation drive capacity is set to low, check that oscillation is stable. Also, if the oscillator manufacturer's
data sheet specifies that a feedback resistor be added external to the chip, insert a feedback resistor between X
CIN
and X
COUT
following the instruction.
Microcomputer
(Built-in feedback resistor)
X
CIN
X
COUT
(Note)
R
Cd
C
CIN
C
COUT
Figure 15. Examples of main clock
Figure 16. Examples of sub clock