UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 192

• Manufacturer Part Number: UPD78F0838
• Description: 8-bit Single-chip Microcontrollers
• Manufacturer: Renesas Electronics Corporation.

5.5 Clock Generator Operation
mode.
the 78K0/Dx2, thus enabling the following.
(1) Enhancement of security function
190
The clock generator generates the following clocks and controls the operation modes of the CPU, such as standby
The CPU starts operation when the on-chip internal high-speed oscillator starts outputting after a reset release in
When the X1 clock is set as the CPU clock by the default setting, the device cannot operate if the X1 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 high-speed oscillation clock, so the device can be started by the internal high-
speed oscillation clock after a reset release. 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.
Main system clock f
Subsystem clock f
Internal low-speed oscillation clock f
CPU clock f
Peripheral hardware clock f
High-speed system clock f
X1 clock f
External main system clock f
Internal high-speed oscillation clock f
XT1 clock f
External subsystem clock f
CPU
X
XT
SUB
MAIN
PRS
IN
EXTS
EXT
Preliminary User’s Manual U19748EJ1V0UD
CHAPTER 5 CLOCK GENERATOR
OSC
OSC8