
CHAPTER 6 CLOCK GENERATOR
User’s Manual U17473EJ2V0UD
123
Figure 6-2. 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
EXCLKS
Note
OSCSELS
Note
0
AMPH
EXCLK
OSCSEL
High-speed system clock
pin operation mode
P121/X1 pin
P122/X2/EXCLK pin
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
External clock input
mode
I/O port
External clock input
AMPH
Operating frequency control
0
1 MHz
≤ fXH ≤ 10 MHz
1
10 MHz < fXH
≤ 20 MHz
Note
EXCLKS and OSCSELS are used in combination with XTSTART (bit 6 of the processor
clock control register (PCC)). See (3) Setting of operation mode for subsystem clock
pin.
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. When the high-speed
system clock (X1 oscillation) is selected as the CPU clock, supply of the CPU
clock is stopped for 4.06 to 16.12
μs after AMPH is set to 1. When the high-
speed system clock (external clock input) is selected as the CPU clock, supply of
the CPU clock is stopped for the duration of 160 external clocks after AMPH is
set to 1.
3. If the STOP instruction is executed when AMPH = 1, supply of the CPU clock is
stopped for 4.06 to 16.12
μs after the STOP mode is released when the internal
high-speed oscillation clock is selected as the CPU clock, or for the duration of
160 external clocks when the high-speed system clock (external clock input) is
selected as the CPU clock. When the high-speed system clock (X1 oscillation) is
selected as the CPU clock, the oscillation stabilization time is counted after the
STOP mode is 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
fXH: High-speed system clock oscillation frequency
<R>