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M16C/64A Group
8.9
Notes on Clock Generator
8.9.1
Oscillator Using a Crystal or a Ceramic Resonator
To connect a crystal/ceramic resonator follow the instructions below:
•
The oscillation characteristics are tied closely to the user's board design. Perform a careful
evaluation of the board before connecting an oscillator.
•
Oscillator structure depends on a crystal/ceramic resonator. The M16C/64A Group MCU contains
a feedback resistor, but an additional external feedback resistor may be required. Contact the
manufacturer of crystal/ceramic resonator regarding circuit constants, as they are dependent on
the a crystal/ceramic resonator or stray capacitance of the mounted circuit.
•
Check output from the CLKOUT pin to confirm that the clock generated by the oscillator is properly
transmitted to the MCU.
The procedure for outputting a clock from the CLKOUT pin is listed below.
Outputting the main clock
(1) Set the PRC0 bit in the PRCR register to 1 (write enabled).
(2) Set the CM11 bit in the CM1 register, the CM07 bit in the CM0 register, and the CM21 bit in the
CM2 register all to 0 (main clock selected).
(3) Select the clock output from the CLKOUT pin (see the table below).
(4) Set the PRC0 bit in the PRCR register to 0 (write disabled).
Table 8.8
Output from CLKOUT Pin When Selecting Main Clock
Bit Setting
PCLKR register
PCLK5 bit
1
0
0
Outputting the sub clock
(1) Set the PRC0 bit in the PRCR register to 1 (write enabled).
(2) Set the CM07 bit in the CM0 register to 1 (sub clock selected).
(3) Set the PCLK5 bit in the PCLKR register to 0, and bits CM01 to CM00 in the CM0 register to 01b
(fC output from CLKOUT pin).
(4) Set the PRC0 bit in the PRCR register to 0 (write disabled).
Figure 8.7
Oscillator Example
R01UH0136EJ0210 Rev.2.10
Jul 31, 2012
CM0 register
Bits CM01 to CM00
00b
10b
11b
MCU
XIN
feedback
XOUT
damping resistor
VSS
Output from the CLKOUT Pin
Clock with the same frequency as the main clock
Main clock divided by 8
Main clock divided by 32
CIN
Rf
Ceramic resonator
or crystal
resistor
Rd
COUT
8. Clock Generator
Page 105 of 800
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