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M16C/5L Group, M16C/56 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.
The main clock, PLL clock, fOCO-F, 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, fOCO-F 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.
8.4.2
Peripheral Function Clocks (f1, fOCO40M, fOCO-F, fOCO-S, fC32, fC, Main
Clock)
f1, fOCO40M, fOCO-F, 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)
•
fOCO-F divided by 1 (no division)
f1 is used for timers A, B, and S, the task monitor timer, real-time clock, UART0 to UART4, multi-master
C-bus interface, and the A/D converter. It also can be used as a sampling clock for NM I, P1_7 digital
2
I
debounce filter.
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.
fOCO40M can be used for the A/D converter. fOCO40M can be used when the F RA00 bit in the FRA0
register is 1 (40 MHz on-chip oscillator on).
fOCO-F can be used for timers A and B, and UART0 to UART4 .
fOCO-F can be used when the FRA00 bit in the FRA0 register is 1 (40 MHz on-chip oscillator on).
fOCO-S is used for timers A and B. It is also used for reset, voltage detector. 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 when the PM25 bit in the PM2 register is 1
(peripheral clock fC provided). fC can be used when the sub clock is on.
The main clock can be used for CAN module.
Figure 8.5 shows Peripheral Function Clocks.
R01UH0127EJ0110 Rev.1.10
Sep 01, 2011
8. Clock Generator
Page 108 of 803
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