r5f21346mnfp Renesas Electronics Corporation., r5f21346mnfp Datasheet - Page 156

• Manufacturer Part Number: r5f21346mnfp
• Description: Single-chip Mcus Incorporates The R8c Cpu Core
• Manufacturer: Renesas Electronics Corporation.

R8C/34M Group
R01UH0131EJ0100 Rev.1.00
Jun 21, 2011
9.4
9.4.1
9.4.2
The on-chip oscillator clock is supplied by the on-chip oscillator (high-speed on-chip oscillator or low-speed on-
chip oscillator). This clock is selected by the FRA01 bit in the FRA0 register.
The clock generated by the low-speed on-chip oscillator is used as the clock source for the CPU clock,
peripheral function clock, fOCO, fOCO-S, and fOCO128.
After a reset, the on-chip oscillator clock generated by the low-speed on-chip oscillator divided by 1 (no
division) is selected as the CPU clock.
If the XIN clock stops oscillating when bits OCD1 to OCD0 in the OCD register are set to 11b, the low-speed
on-chip oscillator automatically starts operating and supplies the necessary clock for the MCU.
The frequency of the low-speed on-chip oscillator varies depending on the supply voltage and the operating
ambient temperature. Application products must be designed with sufficient margin to allow for frequency
changes.
The clock generated by the high-speed on-chip oscillator is used as the clock source for the CPU clock,
peripheral function clock, fOCO, fOCO-F, fOCO40M, and fOCO128.
To use the high-speed on-chip oscillator clock as the clock source for the CPU clock, peripheral clock, fOCO,
and fOCO-F, set bits FRA20 to FRA22 in the FRA2 register as follows:
After a reset, the on-chip oscillator clock generated by the high-speed on-chip oscillator stops. Oscillation is
started by setting the FRA00 bit in the FRA0 register to 1 (high-speed on-chip oscillator on).
Frequency correction data is stored in registers FRA4 to FRA7.
To adjust the frequency of the high-speed on-chip oscillator clock to 36.864 MHz, first transfer the correction
value in the FRA4 register to the FRA1 register and the correction value in the FRA5 register to the FRA3
register before using the values. This enables the setting errors of bit rates such as 9600 bps and 38400 bps to be
0% when the serial interface is used in UART mode (refer to Table 22.8 and Table 23.8 Bit Rate Setting
Example in UART Mode).
To adjust the frequency of the high-speed on-chip oscillator clock to 32 MHz, first transfer the correction value
in the FRA6 register to the FRA1 register and the correction value in the FRA7 register to the FRA3 register
before using the values.
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All division mode can be set when VCC = 2.7 V to 5.5 V
Divide ratio of 8 or more when VCC = 1.8 V to 5.5 V
On-Chip Oscillator Clock
Low-Speed On-Chip Oscillator Clock
High-Speed On-Chip Oscillator Clock
000b to 111b
110b to 111b (divide by 8 or more)
9. Clock Generation Circuit
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