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M16C/5L Group, M16C/56 Group
8.3.3
fOCO40M
fOCO40M is a 40 MHz clock (approx.) supplied by the 40 MHz on-chip oscillator. It is the clock source
for φ AD in the A/D converter.
Follow the steps below to start or stop the 40 MHz on-chip oscillator clock. Refer to 8.2 "Registers" for
details on register and bit access.
40 MHz on-chip oscillator start
(1) Set the FRA00 bit in the FRA0 register to 1 (40 MHz on-chip oscillator on).
(2) Wait for tsu(fOCO40M).
40 MHz on-chip oscillator stop
(1) Set the FRA01 bit in the FRA0 register to 0 (125 MHz on-chip oscillator) (when the CM27 bit is 1
(oscillator stop/restart detect interrupt)).
(2) Set the FRA00 bit in the FRA0 register to 0 (40 MHz on-chip oscillator off).
8.3.4
fOCO-F
fOCO-F is a 40 MHz clock (approx.) supplied by the 40 MHz on-chip oscillator, and divided by the
selected values of bits FRA22 to FRA20 in the FRA2 register. It is the clock source for the CPU and
peripheral function clocks.
After reset, fOCO-F is stopped.
If the main clock stops oscillating and the FRA01 bit is 1 when the CM20 bit in the CM2 register is 1
(oscillator stop/restart detect function enabled), and the CM27 bit is 1 (oscillator stop/restart detect
interrupt), fOCO-F is used as the clock source for the CPU.
Refer to 8.3.3 "fOCO40M" to start or stop the 40 MHz on-chip oscillator clock.
8.3.5
125 kHz On-Chip Oscillator Clock (fOCO-S)
This clock is approximately 125 kHz, and is supplied by the 125 kHz on-chip oscillator. It is used as the
clock source for the CPU and peripheral function clocks. In addition, when the CSPRO bit in the CSPR
register is 1 (count source protection mode enabled), this clock is used as the count source for the
watchdog timer (refer to 13.4.3 "Count Source Protection Mode Enabled").
After reset, fOCO-S divided by 8 becomes the CPU clock.
If the main clock stops oscillating and the FRA01 bit is 0, when the CM20 bit in the CM2 register is 1
(oscillator stop/restart detect function enabled) and the CM27 bit is 1 (oscillator stop/restart detect
interrupt), the 125 kHz on-chip oscillator automatically starts operating and supplying the necessary
clock for the MCU.
Follow the steps below to start or stop fOCO-S. Refer to 8.2 "Registers" for details on register and bit
access.
To start fOCO-S:
(1) Set the CM14 bit in the CM1 register to 0 (125 kHz on-chip oscillator on).
(2) Wait for tsu(fOCO-S).
To start fOCO-S:
(1) Set the CM14 bit in the CM1 register to 1 (125 kHz on-chip oscillator off).
When the CM21 bit is 1 (on-chip oscillator used as the clock source for the CPU), the CM14 bit
becomes 0 (125 kHz on-chip oscillator on).
R01UH0127EJ0110 Rev.1.10
Sep 01, 2011
8. Clock Generator
Page 106 of 803
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