When Subsystem Clock Is Not Used; Internal High-Speed Oscillator; Internal Low-Speed Oscillator; Prescaler - NEC 78K0 Series User Manual

6.4.3 When subsystem clock is not used

If it is not necessary to use the subsystem clock for low power consumption operations, or if not using the
subsystem clock as an I/O port, set the XT1 and XT2 pins to I/O mode (OSCSELS = 0) and connect them as follows.
Input (PM123/PM124 = 1):
Output (PM123/PM124 = 0): Leave open.
Remark OSCSELS:
PM123, PM124: Bits 3 and 4 of port mode register 12 (PM12)

6.4.4 Internal high-speed oscillator

The internal high-speed oscillator is incorporated in the 78K0/KE2. Oscillation can be controlled by the internal
oscillation mode register (RCM).
After a reset release, the internal high-speed oscillator automatically starts oscillation (8 MHz (TYP.)).

6.4.5 Internal low-speed oscillator

The internal low-speed oscillator is incorporated in the 78K0/KE2.
The internal low-speed oscillation clock is only used as the watchdog timer and the clock of 8-bit timer H1. The
internal low-speed oscillation clock cannot be used as the CPU clock.
"Can be stopped by software" or "Cannot be stopped" can be selected by the option byte. When "Can be stopped
by software" is set, oscillation can be controlled by the internal oscillation mode register (RCM).
After a reset release, the internal low-speed oscillator automatically starts oscillation, and the watchdog timer is
driven (240 kHz (TYP.)) if the watchdog timer operation is enabled using the option byte.

6.4.6 Prescaler

The prescaler generates various clocks by dividing the main system clock when the main system clock is selected
as the clock to be supplied to the CPU.
CHAPTER 6 CLOCK GENERATOR
Independently connect to V
Bit 4 of clock operation mode select register (OSCCTL)
Preliminary User's Manual U17260EJ3V1UD
or V via a resistor.
DD SS
149