
R8C/3GM Group
9. Clock Generation Circuit
R01UH0284EJ0100 Rev.1.00
Aug 09, 2011
9.
Clock Generation Circuit
The following five circuits are incorporated in the clock generation circuit:
XIN clock oscillation circuit
XCIN clock oscillation circuit
Low-speed on-chip oscillator
High-speed on-chip oscillator
Low-speed on-chip oscillator for watchdog timer
9.1
Overview
Notes:
1. These pins can be used as P4_6 or P4_7 when using the on-chip oscillator clock as the CPU clock while the
XIN clock oscillation circuit and the XCIN clock oscillation circuit are not used.
2. To input an external clock, set the CM05 bit in the CM0 register to 1 (XIN clock stops), the CM11 bit in the CM1
register to 1 (internal feedback resistor disabled), and the CM13 bit to 1 (XIN-XOUT pin).
3. The clock frequency is automatically set to up to approx. 20 MHz by a divider when using the high-speed on-
chip oscillator as the CPU clock source.
4. This applies when the CSPROINI bit in the OFS register is set to 1 (count source protection mode disabled after reset).
5. This applies when the CSPROINI bit in the OFS register is set to 0 (count source protection mode enabled after reset).
Table 9.1
Specification Overview of Clock Generation Circuit
Item
XIN Clock
Oscillation Circuit
XCIN Clock
Oscillation Circuit
On-Chip Oscillator
Low-Speed On-
Chip Oscillator for
Watchdog Timer
High-Speed
On-Chip Oscillator
Low-Speed
On-Chip Oscillator
Applications
CPU clock
source
Peripheral
function clock
source
CPU clock
source
Peripheral
function clock
source
CPU clock
source
Peripheral
function clock
source
CPU and
peripheral function
clock source when
XIN clock stops
oscillating
CPU clock
source
Peripheral
function clock
source
CPU and
peripheral function
clock source when
XIN clock stops
oscillating
Watchdog timer
clock source
Clock frequency 0 to 20 MHz
32.768 kHz
Approx. 40 MHz
(3) Approx. 125 kHz
Approx. 125 kHz
Connectable
oscillator
Ceramic
resonator
Crystal
oscillator
Crystal
oscillator
Oscillator
connect pins
Oscillation stop,
restart function
Usable
Oscillator status
after reset
Stop
Oscillate
Others
Externally
generated clock
Externally
generated clock
can be input
On-chip
feedback resistor
Rf (connected/
not connected
selectable)