NEC mPD78F0730, Preliminary User'S Manual

Page: 100 / 518

CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
100
<4> 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 22 ELECTRICAL SPECIFICATIONS (TARGET)).
(2) Example of setting procedure when using the external main system clock
<1> Setting frequency (OSCCTL register)
Using AMPH, set the frequency to be used.
AMPH
Note
Operating Frequency Control
0 f
XH
≤
10 MHz
1 10 MHz < f
XH
Note Set AMPH before setting the peripheral functions after a reset release. The value of AMPH can
be changed only once after a reset release. When AMPH is set to 1, the clock supply to the CPU
is stopped for 5
µ
s (MIN.).
Remark f
XH
: High-speed system clock oscillation frequency
<2> Setting P121/X1 and P122/X2/EXCLK pins and selecting operation mode (OSCCTL register)
When EXCLK and OSCSEL are set to 1, the mode is switched from port mode to external clock input
mode.
EXCLK OSCSEL Operation Mode of High-
Speed System Clock Pin
P121/X1 Pin P122/X2/EXCLK Pin
1 1 External clock input mode I/O port External clock input
<3> Controlling external main system clock input (MOC register)
When MSTOP is cleared to 0, the input of the external main system clock is enabled.
Cautions 1. Do not change the value of EXCLK and OSCSEL while the external main system clock is
operating.
2. Set the external main system clock after the supply voltage has reached the operable
voltage of the clock to be used (see CHAPTER 22 ELECTRICAL SPECIFICATIONS
(TARGET)).
(3) Example of setting procedure when using high-speed system clock as CPU clock and peripheral
hardware clock
<1> Setting high-speed system clock oscillation
Note
(See 5.6.1 (1) Example of setting procedure when oscillating the X1 clock and (2) Example of
setting procedure when using the external main system clock. )
Note The setting of <1> is not necessary when high-speed system clock is already operating.
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