User guide

12
SmartBook for Renesas R8C/Tiny Microcontrollers
www.MightyMicons.com
clock to the high speed main clock source. This versatile
clock generating circuit is managed using a set of
registers. The clock generator also contains a set of
dividers to generate many clock derivatives to suit different
operating conditions.
2.2 Main Clock:
The micon gets its main clock from the externally connected crystal
between the pins, XIN and XOUT. This clock can be used as the source
for the CPU and the peripheral functions. This main clock oscillating circuit
can also get externally generated clock at the XIN pin. This oscillating circuit
contains a feedback resistor, which can be disconnected from the oscillator to
reduce the power consumption during the Stop mode. The following figure shows
external clock generating options.
During reset and after reset, the main clock is turned off.
The main clock starts oscillating when the CM05 bit in the CM0 register is set to
“0” (main clock on) after setting the CM13 bit in the CM1 register to “1”.
To use the main clock for the CPU clock, set the OCD2 bit in the OCD register to
“0” (selecting main clock) after the main clock becomes oscillating stably.
The power consumption can be reduced by setting the CM05 bit in the CM0 register
to “1” (main clock off) if the OCD2 bit is set to “1” (On-chip Oscillator clock
selected). Note that if an externally generated clock is fed into the XIN pin, the
main clock cannot be turned off by setting the CM05 bit to “1”. If necessary, use
an external circuit to turn off the clock.
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The micon contains
low speed Ring
Oscillator of about
125KHz and the
high speed Ring
oscillator capable of generating the
nominal clock signal of 8MHz
with the facility to vary the
same from 5 MHz to
16 MHz.