Cpu Clock And Peripheral Function Clock; System Clock; Cpu Clock; Peripheral Function Clock (F1, F2, F4, F8, F32) - Renesas R8C Series User Manual

R8C/1A Group, R8C/1B Group
10.3

CPU Clock and Peripheral Function Clock

There are a CPU clock to operate the CPU and a peripheral function clock to operate the peripheral functions. Refer
to Figure 10.1 Clock Generation Circuit.
10.3.1

System Clock

The system clock is the clock source for the CPU and peripheral function clocks. Either the main clock or the
on-chip oscillator clock can be selected.
10.3.2

CPU Clock

The CPU clock is an operating clock for the CPU and watchdog timer.
The system clock can be divided by 1 (no division), 2, 4, 8, or 16 to produce the CPU clock. Use the CM06 bit
in the CM0 register and bits CM16 to CM17 in the CM1 register to select the value of the division.
After reset, the low-speed on-chip oscillator clock divided by 8 provides the CPU clock. When entering stop
mode from high-speed or medium-speed mode, the CM06 bit is set to 1 (divide-by-8 mode).
10.3.3

Peripheral Function Clock (f1, f2, f4, f8, f32)

The peripheral function clock is the operating clock for the peripheral functions.
The clock fi (i = 1, 2, 4, 8, and 32) is generated by the system clock divided by i. The clock fi is used for timers
X, Y, Z, and C, the serial interface and the A/D converter.
When the WAIT instruction is executed after setting the CM02 bit in the CM0 register to 1 (peripheral function
clock stops in wait mode), the clock fi stops.
10.3.4

fRING and fRING128

fRING and fRING128 are operating clocks for the peripheral functions.
fRING runs at the same frequency as the on-chip oscillator clock and can be used as the source for timer X.
fRING128 is generated from fRING by dividing it by 128, and it can be used as timer C.
When the WAIT instruction is executed, the clocks fRING and fRING128 do not stop.
10.3.5

fRING-fast

fRING-fast is used as the count source for timer C. fRING-fast is generated by the high-speed on-chip oscillator
and supplied by setting the HRA00 bit to 1.
When the WAIT instruction is executed, the clock fRING-fast does not stop.
10.3.6

fRING-S

fRING-S is an operating clock for the watchdog timer and voltage detection circuit. fRING-S is supplied by
setting the CM14 bit to 0 (low-speed on-chip oscillator on) and uses the clock generated by the low-speed on-
chip oscillator. When the WAIT instruction is executed or in count source protect mode of the watchdog timer,
fRING-S does not stop.
Rev.1.30 Dec 08, 2006
REJ09B0252-0130
Page 67 of 315
10. Clock Generation Circuit