upd78f0124hgba1-8et-a Renesas Electronics Corporation., upd78f0124hgba1-8et-a Datasheet - Page 108

• Manufacturer Part Number: upd78f0124hgba1-8et-a
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

5.5 Clock Generator Operation
mode.
thus enabling the following.
(1) Enhancement of security function
(2) Improvement of performance
108
The clock generator generates the following clocks and controls the operation modes of the CPU, such as standby
• High-speed system clock f
• Internal oscillation clock f
• Subsystem clock f
• CPU clock f
• Clock to peripheral hardware
The CPU starts operation when the on-chip internal oscillator starts outputting after reset release in the 78K0/KD1+,
When the high-speed system clock is set as the CPU clock by the default setting, the device cannot operate if the
high-speed system clock is damaged or badly connected and therefore does not operate after reset is released.
However, the start clock of the CPU is the on-chip internal oscillation clock, so the device can be started by the
internal oscillation clock after reset release by the clock monitor (detection of high-speed system clock stop).
Consequently, the system can be safely shut down by performing a minimum operation, such as acknowledging a
reset source by software or performing safety processing when there is a malfunction.
Because the CPU can be started without waiting for the high-speed system clock oscillation stabilization time, the
total performance can be improved.
A timing diagram of the CPU default start using internal oscillator is shown in Figure 5-12.
CPU
XT
R
XP
CHAPTER 5 CLOCK GENERATOR
User’s Manual U16962EJ3V0UD