Renesas rl78 Manuel D’Utilisation
RL78/G1A
CHAPTER 5 CLOCK GENERATOR
R01UH0305EJ0200 Rev.2.00
144
Jul 04, 2013
Figure 5-2. Format of Clock Operation Mode Control Register (CMC)
Address: FFFA0H After reset: 00H R/W
Symbol
7 6 5 4 3 2 1 0
CMC EXCLK
OSCSEL
EXCLKS
OSCSELS
0 AMPHS1
AMPHS0
AMPH
EXCLK
OSCSEL
High-speed system clock
pin operation mode
X1/P121 pin
X2/EXCLK/P122 pin
0
0
Input port mode
Input port
0
1
X1 oscillation mode
Crystal/ceramic resonator connection
1
0
Input port mode
Input port
1
1
External clock input mode
Input port
External clock input
EXCLKS
OSCSELS
Subsystem
clock
pin
operation mode
XT1/P123 pin
XT2/EXCLKS/P124 pin
0
0
Input port mode
Input port
0
1
XT1 oscillation mode
Crystal resonator connection
1
0
Input port mode
Input port
1
1
External clock input mode
Input port
External clock input
AMPHS1
AMPHS0
XT1 oscillator oscillation mode selection
0
0
Low power consumption oscillation (default)
0 1
Normal
oscillation
1
0
Ultra-low power consumption oscillation
1 1
Setting
prohibited
AMPH
Control of X1 clock oscillation frequency
0
1
MHz
≤ f
X
≤ 10 MHz
1
10 MHz < f
X
≤ 20 MHz
Cautions 1. The CMC register can be written only once after reset release, by an 8-bit memory
manipulation instruction. When using the CMC register with its initial value (00H), be
sure to set the register to 00H after a reset ends in order to prevent malfunction due
to a program loop. Such a malfunction becomes unrecoverable when a value other
than 00H is mistakenly written.
2. After reset release, set the CMC register before X1 or XT1 oscillation is started as set
by the clock operation status control register (CSC).
3. Be sure to set the AMPH bit to 1 if the X1 clock oscillation frequency exceeds 10 MHz.
4. Specify the settings for the AMPH, AMPHS1, and AMPHS0 bits while f
IH
is selected as
f
CLK
after a reset ends (before f
CLK
is switched to f
MX
or f
SUB
).
5. Oscillation stabilization time of f
XT
, counting on the software.
6. Although the maximum system clock frequency is 32 MHz, the maximum frequency
of the X1 oscillator is 20 MHz.
(Cautions and Remark are given on the next page.)