Renesas rl78 User Manual

Page of 1004
 
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 
 
Input port mode 
Input port 
 
X1 oscillation mode 
Crystal/ceramic resonator connection 
 
Input port mode 
Input port 
 
External clock input mode
Input port 
External clock input 
 
 EXCLKS 
OSCSELS 
Subsystem 
clock 
pin 
operation mode 
XT1/P123 pin 
XT2/EXCLKS/P124 pin
 
Input port mode 
Input port  
 
XT1 oscillation mode 
Crystal resonator connection 
 
Input port mode 
Input port 
 
External clock input mode
Input port 
External clock input 
 
 
AMPHS1 
AMPHS0 
XT1 oscillator oscillation mode selection
 
 
 
Low power consumption oscillation (default)  
 0 1 
Normal 
oscillation 
 
Ultra-low power consumption oscillation 
 1 1 
Setting 
prohibited 
 
 
AMPH 
Control of X1 clock oscillation frequency  
 0 
MHz 
≤ f
X
 
≤ 10 MHz 
 
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.)