UPD78F0838 Renesas Electronics Corporation., UPD78F0838 Datasheet - Page 175

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

5.1 Functions of Clock Generator
The clock generator generates the clock to be supplied to the CPU and peripheral hardware.
The following system clocks and clock oscillators are selectable.
(1) Main system clock
(2) Subsystem clock
(3) Internal low-speed oscillation clock (clock for watchdog timer)
Remarks 1. f
<1> X1 oscillator
<2> Internal high-speed oscillator
An external main system clock (f
system clock, a high-speed system clock (X1 clock or external main system clock) or internal high-speed
oscillation clock can be selected by using the main clock mode register (MCM).
An external subsystem clock (f
Subsystem clock oscillator
This circuit oscillates at a frequency of f
and XT2.
operation mode select register (OSCCTL).
Internal low-speed oscillator
This circuit oscillates a clock of f
oscillation clock always starts operating.
Oscillation can be stopped by using the internal oscillation mode register (RCM) when “internal low-speed
oscillator can be stopped by software” is set by option byte.
The internal low-speed oscillation clock cannot be used as the CPU clock. The following hardware operates
with the internal low-speed oscillation clock.
Watchdog timer
8-bit timer TM50 (when f
This circuit oscillates a clock of f
instruction or using the main OSC control register (MOC).
This circuit oscillates a clock of f
operating with this internal high-speed oscillation clock. Oscillation can be stopped by executing the
STOP instruction or using the internal oscillator mode register (RCM).
2. f
3. f
4. f
5. f
6. f
X
OSC8
EXT
XT
EXTS
OSC
:
:
Oscillation can be stopped by using the processor clock control register (PCC) and clock
:
:
:
:
X1 clock oscillation frequency
Internal high-speed oscillation clock frequency
External main system clock frequency
XT1 clock oscillation frequency
External subsystem clock frequency
Internal low-speed oscillation clock frequency
OSC
CHAPTER 5 CLOCK GENERATOR
EXTS
, f
EXT
OSC
Preliminary User’s Manual U19748EJ1V0UD
= 32.768 kHz) can also be supplied from the EXCLKS pin.
/2
= 4 to 20 MHz) can also be supplied from the EXCLK pin. As the main
OSC
7
OSC8
, or f
X
= 4 to 20 MHz. Oscillation can be stopped by executing the STOP
= 240 kHz (TYP.). After a reset release, the internal low-speed
XT
OSC
= 8 MHz (TYP.). After a RESET release, the CPU always starts
= 32.768 kHz by connecting a 32.768 kHz resonator across XT1
/2
9
is selected)
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