对于R8C单片机，系统上电时，默认的CPU时钟为内部低速振荡器的8分频
可由下列步骤切换至内部高速振荡器

/* change low speed OCO to high speed OCO */
void clock_init_highoco(void)
{
 unsigned int i=0;
 prc0 = 1;  // Release protection
 hra00 = 1;  // High OCO oscillates
 while(i<500) i++;
 hra01 = 1;  // Select High_OCO/8 as CPU clock
 cm16 = 0;  // no division
 cm17 = 0;
 cm06 = 0;  // Select High_OCO as CPU clock
 while(i<500) i++;
 cm14 = 1;  // Stop Low_OCO
 while(i<500) i++;
 prc0 = 1;  // Set protection 
}