M32C80 Datasheet, PDF (84/352 Pages) Renesas Technology Corp – 16/32-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M32C/80 SERIES

M32C/80 Group
8. Clock Generation Circuit
8.1.1 Main Clock
Main clock oscillation circuit generates the main clock. The main clock becomes clock source of the CPU
clock and peripheral function clock.
The main clock oscillation circuit is configured by connecting an oscillator or resonator between the XIN
and XOUT pins. The circuit has a built-in feedback resistor. The feedback resistor is separated from the
oscillation circuit in stop mode to reduce power consumption. An external clock can be applied to the XIN
pin in the main clock oscillation circuit. Figure 8.9 shows an example of a main clock circuit connection.
Circuit constants vary depending on each oscillator. Use the circuit constant recommended by each oscil-
lator manufacturer.
The main clock divided-by-eight becomes a CPU clock source after reset.
To reduce power consumption, set the CM05 bit in the CM0 register to "1" (main clock stopped) after
switching the CPU clock source to the sub clock or on-chip oscillator clock. In this case, the clock applied
to XOUT becomes high ("H"). XIN is pulled up by XOUT via the feedback resistor which remains on. When
an external clock is applied to the XIN pin, do not set the CM05 bit to "1".
All clocks, including the main clock, stop in stop mode. Refer to 8.5 Power Consumption Control for
details.
Microcomputer
(Built-in Feedback Resistor)
XIN
Oscillator
XOUT
VSS
Rd⁽¹⁾
Microcomputer
(Built-in Feedback Resistor)
CIN
XIN
External Clock
VCC
VSS
COUT
XOUT Open
NOTE:
1. Place a damping resistor if required. Resistance values vary depending on the oscillator setting.
Use values recommended by each oscillator manufacturer.
Place a feedback resistor between XIN and XOUT if the oscillator manufacturer recommends
placing the resistor externally.
Figure 8.9 Main Clock Circuit Connection
Rev. 1.00 Nov. 01, 2005 Page 65 of 330
REJ09B0271-0100