UPD78F0411GA-GAM-AX Datasheet, PDF (129/564 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

CHAPTER 5 CLOCK GENERATOR
Remark While the microcontroller is operating, a clock that is not used as the CPU clock can be stopped via
software settings. The internal high-speed oscillation clock and high-speed system clock can be
stopped by executing the STOP instruction (see (4) in 5.6.1 Example of controlling high-speed
system clock, (3) in 5.6.2 Example of controlling internal high-speed oscillation clock, and (4) in
5.6.3 Example of controlling subsystem clock).
5.6 Controlling Clock
5.6.1 Example of controlling high-speed system clock
The following two types of high-speed system clocks are available.
• X1 clock:
Crystal/ceramic resonator is connected across the X1 and X2 pins.
• External main system clock: External clock is input to the EXCLK pin.
When the high-speed system clock is not used, the OCD0A/X1/P121 and OCD0B/X2/EXCLK/P122 pins can be
used as I/O port pins.
Caution The OCD0A/X1/P121 and OCD0B/X2/EXCLK/P122 pins are in the I/O port mode after a reset
release.
The following describes examples of setting procedures for the following cases.
(1) When oscillating X1 clock
(2) When using external main system clock
(3) When using high-speed system clock as CPU clock and peripheral hardware clock
(4) When stopping high-speed system clock
(1) Example of setting procedure when oscillating the X1 clock
<1> Setting P121/X1 and P122/X2/EXCLK pins and selecting X1 clock or external clock (OSCCTL register)
When EXCLK is cleared to 0 and OSCSEL is set to 1, the mode is switched from port mode to X1
oscillation mode.
EXCLK
0
OSCSEL
1
Operation Mode of High-
Speed System Clock Pin
X1 oscillation mode
P121/X1 Pin
P122/X2/EXCLK Pin
Crystal/ceramic resonator connection
<2> Controlling oscillation of X1 clock (MOC register)
If MSTOP is cleared to 0, the X1 oscillator starts oscillating.
<3> Waiting for the stabilization of the oscillation of X1 clock
Check the OSTC register and wait for the necessary time.
During the wait time, other software processing can be executed with the internal high-speed oscillation
clock.
Cautions 1. Do not change the value of EXCLK and OSCSEL while the X1 clock is operating.
2. Set the X1 clock after the supply voltage has reached the operable voltage of the clock to
be used (see CHAPTER 27 ELECTRICAL SPECIFICATIONS (STANDARD PRODUCTS)).
User’s Manual U18698EJ1V0UD
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