M32C80 Datasheet, PDF (85/352 Pages) Renesas Technology Corp – 16/32-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M32C/80 SERIES

M32C/80 Group
8. Clock Generation Circuit
8.1.2 Sub Clock
Sub clock oscillation circuit generates the sub clock. The sub clock becomes clock source of the CPU
clock and for the timers A and B. The same frequency, fc, 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 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 XCIN
pin. Figure 8.10 shows an example of a sub clock circuit connection. Circuit constants vary depending on
each oscillator. Use the circuit constant recommended by each oscillator manufacturer.
The sub clock stops after reset. The feedback resistor is separated from the oscillation circuit. When the
PD8_6 and PD8_7 bits in the PD8 register are set to "0" (input mode) and the PU25 bit in the PUR2
register is set to "0" (no pull-up), set the CM04 bit in the CM0 register to "1" (XCIN-XCOUT oscillation
function). The sub clock oscillation circuit starts oscillating. To apply an external clock to the XCIN pin, set
the CM04 bit to "1" when the PD8_7 bit is set to "0" and the PU25 bit to "0". The clock applied to the XCIN
pin becomes a clock source of the sub clock.
When the CM07 bit in the CM0 register is set to "1" (sub clock) after the sub clock oscillation has stabi-
lized, the sub clock becomes a CPU clock source.
All clocks, including the sub clock, stop in stop mode. Refer to 8.5 Power Consumption Control for
details.
Microcomputer
(Built-in Feedback Resistor)
XCIN
Oscillator
XCOUT
VSS
RCd⁽¹⁾
CCIN
Microcomputer
(Built-in Feedback Resistor)
XCIN
External Clock
VCC
VSS
CCOUT
XCOUT 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 XCIN and XCOUT if the oscillator manufacturer recommends
placing the resistor externally.
Figure 8.10 Sub Clock Circuit Connection
Rev. 1.00 Nov. 01, 2005 Page 66 of 330
REJ09B0271-0100