UPD78F1502AGK-GAK-AX Datasheet, PDF (242/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 5 CLOCK GENERATOR
5.4.3 Internal high-speed oscillator
The internal high-speed oscillator is incorporated in the 78K0R/Lx3 (1, 8 and 20 MHz (TYP.)). Oscillation can be
controlled by bit 0 (HIOSTOP) of the clock operation status control register (CSC) and bit 0 (DSCON) of the 20 MHz
internal high-speed oscillation control register (DSCCTL).
Caution To use the 1, 8, or 20 MHz internal high-speed oscillation clock, use the option byte to set the frequency
in advance (for details, see CHAPTER 26 OPTION BYTE). Also, the internal high-speed oscillator
automatically starts oscillating after reset release. (If 8 MHz or 20 MHz is selected by using the option
byte, the microcontroller operates using the 8 MHz internal high-speed oscillator.) To use the 20 MHz
internal high-speed oscillator to operate the microcontroller, oscillation is started by setting bit 0
(DSCON) of the DSCCTL register to 1 with VDD ≥ 2.7 V.
5.4.4 Internal low-speed oscillator
The internal low-speed oscillator is incorporated in the 78K0R/Lx3 microcontrollers.
The internal low-speed oscillation clock is used only as the watchdog timer clock. The internal low-speed oscillation
clock cannot be used as the CPU clock.
After a reset release, the internal low-speed oscillator automatically starts oscillation, and the watchdog timer is driven
(30 kHz (TYP.)) if the watchdog timer operation is enabled by the option byte.
The internal low-speed oscillator continues oscillation except when the watchdog timer stops. When the watchdog
timer operates, the internal low-speed oscillation clock does not stop, even in case of a program loop.
5.4.5 Prescaler
The prescaler generates a CPU/peripheral hardware clock by dividing the main system clock and subsystem clock.
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Jun 20, 2011