Datasheet

78K0/Kx2-L CHAPTER 5 CLOCK GENERATOR
R01UH0028EJ0400 Rev.4.00 216
Sep 27, 2010
Figure 5-15. Examples of Incorrect Resonator Connection (2/2)
(e) Signals are fetched
VSS X1 X2
Remark When using the subsystem clock, replace X1 and X2 with XT1 and XT2, respectively. Also, insert resistors
in series on the XT2 side.
Caution 2. When X2 and XT1 are wired in parallel, the crosstalk noise of X2 may increase with XT1, resulting
in malfunctioning.
5.4.3 When subsystem clock is not used
If it is not necessary to use the subsystem clock
Note
for low power consumption operations, watch operations, etc., or if
not using the subsystem clock as an Input port, set the XT1 and XT2 pins to Input mode (OSCSELS = 0) and
independently connect to V
DD or VSS via a resistor.
Note 78K0/KC2-L only
5.4.4 Internal high-speed oscillator
The internal high-speed oscillator is incorporated in the 78K0/Kx2-L microcontrollers. Oscillation can be controlled by
the internal oscillation mode register (RCM).
After a reset release, the internal high-speed oscillator automatically starts oscillation.
Internal high-speed oscillation clock frequency (4 MHz (TYP.)/8 MHz (TYP.)) can be set by the option byte.
5.4.5 Internal low-speed oscillator
The internal low-speed oscillator is incorporated in the 78K0/Kx2-L microcontrollers.
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
(30 kHz (TYP.)) if the watchdog timer operation is enabled using the option byte.
5.4.6 Prescaler
The prescaler generates the CPU clock by dividing the main system clock when the main system clock is selected as
the clock to be supplied to the CPU.