Clock Generation Circuit
59
Mitsubishi microcomputers
M16C / 62P Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
development
Preliminary Specifications Rev.1.0
Specifications in this manual are tentative and subject to change.
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 1.9.8. Examples of Sub Clock Connection Circuit
(2) Sub Clock
The sub clock is generated by the sub clock oscillation circuit. This clock is used as the clock source for
the CPU clock, as well as the timer A and timer B count sources. In addition, an fc clock with the same
frequency as that of the sub clock can be output from the CLK
OUT
pin.
The sub clock oscillator circuit is configured by connecting a crystal resonator between the X
CIN
and
X
COUT
pins. The sub clock oscillator circuit contains a feedback resistor, which is disconnected from the
oscillator circuit during stop mode in order to reduce the amount of power consumed in the chip. The sub
clock oscillator circuit may also be configured by feeding an externally generated clock to the X
CIN
pin.
Figure 1.9.8 shows the examples of sub clock connection circuit.
After reset, the sub clock is turned off. At this time, the feedback resistor is disconnected from the oscilla-
tor circuit.
To use the sub clock for the CPU clock, set the CM07 bit of CM0 register to “1 ” (sub clock) after the sub
clock becomes oscillating stably.
During stop mode, all clocks including the sub clock are turned off. Refer to “power control”.