M16C65 Datasheet, PDF (153/829 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/60

Under development
M16C/65 Group
Preliminary Specification
This is a preliminary specification and is subject to change.
8. Clock Generator
8.3.6 Sub Clock (fC)
The sub clock is supplied by the sub clock oscillator circuit. This clock is used as the clock source for
count sources of the CPU clock, timer A, timer B, real-time clock, CEC function, and remote control
signal receiver.
The sub clock oscillator circuit is configured by connecting a crystal resonator between pins XCIN and
XCOUT. The sub clock oscillator circuit contains a feedback resistor, which is disconnected from the
oscillation circuit in stop mode in order to reduce the amount of power consumed by the chip. The sub
clock oscillator circuit may also be configured by feeding an externally generated clock to the XCIN pin.
Figure 8.4 shows Sub Clock Connection Examples.
MCU
(Built-in feedback resistor)
XCIN
CCIN
Oscillator
XCOUT
VSS
RCd ⁽¹⁾
CCOUT
MCU
(Built-in feedback resistor)
XCIN
External clock
VCC1
VSS
XCOUT Open
Note :
1. Insert a damping resistor if required. The resistance will vary depending on the oscillator and the
oscillation drive capacity setting. Use the value recommended by the oscillator manufacturer.
When the oscillation drive capacity is set to low, check if oscillation is stable in low status. Also, place
a feedback resistor between XCIN and XCOUT if the oscillator manufacturer recommends placing the
resistor externally.
Figure 8.4 Sub Clock Connection Examples
After reset, the sub clock is stopped. At this time, the feedback resistor is disconnected from the
oscillator circuit.
Follow the steps below to start the sub clock. Refer to 8.2 “Registers” for access to registers and bits.
(1)Set the PU21 bit in the PUR2 register to 0 (P8_4 to P8_7 not pulled high).
(2)Set bits PD8_6 and PD8_7 in the PD8 register to 0 (P8_6, P8_7 function as input ports).
(3)Set the CM04 bit to 1 (XCIN-XCOUT oscillation function). Set the CM03 bit to 1 (XCIN-XCOUT
drive capacity high).
(4)Wait until sub clock oscillation stabilizes (enter the external clock when entering it from the XCIN
pin).
REJ09B0484-0030 Rev.0.30 Sep 09, 2008
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