RL78/G1P
CHAPTER 5 CLOCK GENERATOR
R01UH0895EJ0100 Rev.1.00
100
Nov 29, 2019
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
0 0 0 0 0
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
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 oscillation is started as set by the
clock operation status control register (CSC).
3. Specify the settings for the AMPH bit while f
IH
is selected as f
CLK
after a reset ends
(before f
CLK
is switched to f
MX
).
4. Although the maximum system clock frequency is 32 MHz, the maximum frequency
of the X1 oscillator is 20 MHz.
Remark
f
X
: X1 clock frequency