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M16C/64A Group
8.4
CPU Clock and Peripheral Function Clocks
The CPU is run by the CPU clock, and the peripheral functions are run by the peripheral function clocks.
8.4.1
CPU Clock and BCLK
The CPU clock is an operating clock for the CPU and watchdog timer. It is also used as a sampling
clock for the NMI / SD digital filter.
The main clock, PLL clock, fOCO-S, or fC can be selected as the clock source for the CPU clock. (See
Table 9.2 "Clocks in Normal Operating Mode".)
When the main clock, PLL clock, or fOCO-S is selected as the clock source for the CPU clock, the
selected clock divided by 1, 2, 4, 8 or 16 becomes the CPU clock. Use the CM06 bit in the CM0 register
and bits CM17 to CM16 in the CM1 register to select a frequency-divided value.
When fC is selected as the clock source for the CPU clock, it is not divided and is used directly as the
CPU clock.
After reset, fOCO-S divided by 8 becomes the CPU clock. Note that when entering stop mode or when
the CM21 bit in the CM2 register is 0 (main clock or PLL clock) and the CM05 bit is 1 (main clock off),
the CM06 bit in the CM0 register becomes 1 (divide-by-8 mode).
BCLK is a bus reference clock.
In memory expansion or microprocessor mode, a BCLK signal with the same frequency as the CPU
clock can be output from the BCLK pin by setting the PM07 bit in the PM0 register to 0 (output
enabled).
8.4.2
Peripheral Function Clocks (f1, fOCO-S, fC32, fC)
f1, fOCO-S, and fC32 are operating clocks for the peripheral functions.
f1 is one of the following:
•
Main clock divided by 1 (no division)
•
PLL clock divided by 1 (no division)
•
fOCO-S divided by 1 (no division)
f1 is used for timers A and B, PWM, real-time clock, remote control signal receiver, UART0 to UART2,
UART5 to UART7, SI/O3, SI/O4, multi-master I
When the WAIT instruction is executed after setting the CM02 bit in the CM0 register to 1 (peripheral
function clock f1 turned off during wait mode), the f1 clock is stopped.
fOCO-S is used for timers A and B. It is also used for reset, voltage detector, and watchdog timer.
fOCO-S is also used when the CM14 bit in the CM1 register is set to 0 (125 kHz on-chip oscillator on).
fC divided by 32 becomes fC32. fC32 is used for timers A and B, and can be used when the sub clock
is on.
fC is used as the count source for the real-time clock, remote control signal receiver, and CEC function
when the PM25 bit in the PM2 register is 1 (peripheral clock fC provided). fC can be used when the sub
clock is on.
Figure 8.5 shows Peripheral Function Clocks.
R01UH0136EJ0210 Rev.2.10
Jul 31, 2012
2
C-bus interface, and the A/D converter.
8. Clock Generator
Page 99 of 800
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