UPD78F1502AGK-GAK-AX Datasheet, PDF (226/1031 Pages) Renesas Technology Corp – 16-Bit Single-Chip Microcontrollers

78K0R/Lx3
CHAPTER 5 CLOCK GENERATOR
Figure 5-2. Format of Clock Operation Mode Control Register (CMC)
Address: FFFA0H After reset: 00H R/W
Symbol
7
6
5
4
3
CMC
EXCLK OSCSEL
0
OSCSELS
0
2
AMPHS1
1
AMPHS0
0
AMPH
EXCLK
0
0
1
1
OSCSEL
0
1
0
1
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
OSCSELS Subsystem clock pin operation mode
0
Input port mode
1
XT1 oscillation mode
XT1/P123 pin
XT2/P124 pin
Input port
Crystal resonator connection
AMPHS1
0
0
1
1
AMPHS0
0
1
0
1
XT1 oscillator oscillation mode selection
Low-consumption oscillation
Normal oscillation
Super-low-consumption oscillation
AMPH
0
1
Control of high-speed system clock oscillation frequency
2 MHz ≤ fMX ≤ 10 MHz
10 MHz < fMX ≤ 20 MHz
Remark fMX: High-speed system clock frequency
Cautions 1. CMC can be written only once after reset release, by an 8-bit memory manipulation
instruction.
2. After reset release, set CMC before X1 or XT1 oscillation is started as set by the
clock operation status control register (CSC).
3. Be sure to set AMPH to 1 if the X1 clock oscillation frequency exceeds 10 MHz.
4. To use CMC with its initial value (00H), be sure to set it to 00H after releasing reset in
order to prevent malfunction when a program loop occurs.
5. The XT1 oscillator is designed as a low-gain circuit for achieving low-power
consumption. Note the following points when designing the XT1 oscillator.
• The pins and circuit board include parasitic capacitance. Therefore, confirm that
there are no problems by performing oscillation evaluation on the circuit board to
be actually used.
• When low-consumption oscillation or super-low-consumption oscillation is
selected, lower power consumption than when selecting normal oscillation can
be achieved. However, in this case, the XT1 oscillation margin is reduced, so
perform sufficient oscillation evaluation of the resonator to be used for XT1
oscillation before using the resonator.
(Cautions are continued on the next page.)
R01UH0004EJ0501 Rev.5.01
210
Jun 20, 2011