19
Clock Generating Circuit
Mitsubishi microcomputers
M30218 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
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
Sub clock generating circuit
Use of clock
CPU’s operating clock source
Internal peripheral units’
Timer A/B’s count clock
operating clock source
source
Usable oscillator
Ceramic or crystal oscillator
Crystal oscillator
Pins to connect oscillator
XIN, XOUT
XCIN, XCOUT
Oscillation stop/restart function
Available
Oscillator status immediately after reset
Oscillating
Stopped
Other
Externally derived clock can be input
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)
XIN
XOUT
Externally derived clock
Open
Vcc
Vss
Microcomputer
(Built-in feedback resistor)
XIN
XOUT
Rd
CIN
COUT
(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 XIN
and XOUT following the instruction.
Microcomputer
(Built-in feedback resistor)
XCIN
XCOUT
Externally derived clock
Open
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 XCIN
and XCOUT following the instruction.
Microcomputer
(Built-in feedback resistor)
XCIN
XCOUT
(Note)
CCIN
CCOUT
RCd
Figure 15. Examples of main clock
Figure 16. Examples of sub clock