M32C8A Datasheet, PDF (96/372 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M32C/80 Series

M32C/8A Group
9. Clock Generation Circuits
9.1.2 Sub Clock
Sub clock oscillation circuit generates the sub clock. The sub clock is used as the clock source for the CPU
clock and for timer A and timer B. fC, which has the same frequency as the sub clock can be output from the
CLKOUT pin.
The sub clock oscillation circuit is configured by connecting a crystal oscillator between the XCIN and
XCOUT 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 sub clock oscillation circuit may also be
configured by feeding an externally generated clock to the XCIN pin. Figure 9.10 shows an example of sub
clock circuit connection. Circuit constants vary depending on each oscillator. Use the circuit constant
recommended by each oscillator manufacturer.
The sub clock is stopped after reset, and the feedback resistor is disconnected from the oscillation circuit. To
start oscillating the sub clock oscillation circuit, set both the PD8_7 and PD8_6 bits in the PD8 register to 0
(input mode), the PU25 bit in the PUR2 register to 0 (no pull-up), and then the CM04 bit in the CM0 register to
1 (XCIN-XCOUT oscillation function). To input the externally generated clock to the XCIN pin, set the PD8_7
bit to 0, the PU25 bit to 0, and then the CM04 bit to 1. A clock input to the XCIN pin becomes the clock source
for the sub clock.
When the CM07 bit in the CM0 register is set to 1 (sub clock) after the sub clock oscillation stabilizes, the sub
clock becomes the CPU clock source.
All clocks, including the sub clock, stop in stop mode. Refer to 9.5 Power Consumption Control for details.
MCU
(On-chip feedback resistor)
XCIN
Oscillator
XCOUT
VSS
RCd⁽¹⁾
CCIN
CCOUT
MCU
(On-chip feedback resistor)
XCIN
Externally generated clock
VCC
VSS
XCOUT 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 XCIN and XCOUT following the instructions.
Figure 9.10 Sub Clock Circuit Connection
Rev.1.00 Jul 15, 2007 Page 79 of 352
REJ09B0385-0100