M32C87 Datasheet, PDF (111/627 Pages) Renesas Technology Corp – MCU M16C FAMILY / M32C/80 SERIES

M32C/87 Group (M32C/87, M32C/87A, M32C/87B)
9. Clock Generation Circuits
9.1.1 Main Clock
Main clock oscillation circuit generates the main clock. The main clock is used as the clock source for the CPU
clock and peripheral function clocks.
The main clock oscillation circuit is configured by connecting an oscillator between the XIN and XOUT pins.
The circuit has an on-chip feedback resistor. The feedback resistor is disconnected from the oscillation circuit in
stop mode to reduce power consumption. The main clock oscillation circuit may also be configured by feeding
an externally generated clock to the XIN pin. Figure 9.9 shows examples of main clock circuit connection.
Circuit constants vary depending on each oscillator. Use the circuit constant recommended by each oscillator
manufacturer.
The main clock divided-by-eight becomes the CPU clock source after reset.
To reduce power consumption, set the CM05 bit in the CM0 register to 1 (main clock stopped) after the sub
clock or on-chip oscillator clock is selected as the CPU clock sources. In this case, the XOUT pin outputs an
“H” signal. The XIN pin is pulled up to the XOUT pin via the feedback resistor which remains on. When an
external clock is input to the XIN pin, do not set the CM05 bit to 1.
All clocks, including the main clock, stop in stop mode. Refer to 9.5 Power Consumption Control for details.
MCU
(On-chip feedback resistor)
XIN
Oscillator
XOUT
Rd⁽¹⁾
VSS
CIN
COUT
MCU
(On-chip feedback resistor)
XIN
Externally generated clock
VCC
VSS
XOUT Open
NOTE:
1. Insert a damping resistor if required. Resistance values vary depending on the oscillator setting. Use the resistance values
recommended by the oscillator manufacturer.
If the oscillator manufacturer recommends that a feedback resistor be added to the chip externally, insert a feedback
resistor between XIN and XOUT following the instructions.
Figure 9.9 Main Clock Circuit Connection
REJ09B0180-0151 Rev.1.51 Jul 31, 2008
Page 89 of 587