CHAPTER 5 CLOCK GENERATOR
Preliminary User’s Manual U19014EJ1V0UD
85
(1) Clock operation mode select register (OSCCTL)
This register selects the operation modes of the high-speed system clock and the gain of the on-chip oscillator.
OSCCTL can be set by a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets this register to 00H.
Figure 5-2. Format of Clock Operation Mode Select Register (OSCCTL)
Address: FF9FH After reset: 00H R/W
Symbol
<7>
<6>
5 4 3 2 1
<0>
OSCCTL EXCLK OSCSEL
0
0 0 0 0
AMPH
EXCLK
OSCSEL
High-speed system clock
pin operation mode
P121/X1 pin
P122/X2/EXCLK pin
0
0
I/O port mode
I/O port
0
1
X1 oscillation mode
Crystal/ceramic resonator connection
1
0
I/O port mode
I/O port
1 1
External
clock
input
mode
I/O port
External clock input
AMPH
Operating frequency control
0
f
XH
≤
10 MHz
1
10 MHz < f
XH
Cautions 1. Be sure to set AMPH to 1 if the high-speed system clock oscillation frequency
exceeds 10 MHz.
2. Set AMPH before setting the peripheral functions after a reset release. The value
of AMPH can be changed only once after a reset release. The clock supply to the
CPU is stopped for 5
µ
s (MIN.) after AMPH has been set to 1.
3. If the STOP instruction is executed with AMPH set to 1 when the internal high-
speed oscillation clock or external main system clock is used as the CPU clock,
then the clock supply to the CPU is stopped for 5
µ
s (MIN.) after the STOP mode
has been released. If the X1 clock is used as the CPU clock, oscillation
stabilization time is counted after the STOP mode has been released.
4. To change the value of EXCLK and OSCSEL, be sure to confirm that bit 7
(MSTOP) of the main OSC control register (MOC) is 1 (the X1 oscillator stops or
the external clock from the EXCLK pin is disabled).
Remark
f
XH
: High-speed system clock oscillation frequency
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