Renesas rl78 User Manual
RL78/G1A
CHAPTER 5 CLOCK GENERATOR
R01UH0305EJ0200 Rev.2.00
146
Jul 04, 2013
5.3.2 System clock control register (CKC)
This register is used to select a CPU/peripheral hardware clock and a main system clock.
The CKC register can be set by a 1-bit or 8-bit memory manipulation instruction.
Reset signal generation sets this register to 00H.
Figure 5-3. Format of System Clock Control Register (CKC)
Address: FFFA4H After reset: 00H R/W
Note 1
Symbol
<7> <6> <5> <4> 3
2
1
0
CKC
CLS
CSS
MCS
MCM0
0 0 0 0
CLS
Status of CPU/peripheral hardware clock (f
CLK
)
0
Main system clock (f
MAIN
)
1
Subsystem
clock
(f
SUB
)
CSS
Selection of CPU/peripheral hardware clock (f
CLK
)
0
Main system clock (f
MAIN
)
1
Note 2
Subsystem
clock
(f
SUB
)
MCS
Status of Main system clock (f
MAIN
)
0
High-speed on-chip oscillator clock (f
IH
)
1
High-speed system clock (f
MX
)
MCM0
Note 2
Main system clock (f
MAIN
) operation control
0
Selects the high-speed on-chip oscillator clock (f
IH
) as the main system clock (f
MAIN
)
1
Selects the high-speed system clock (f
MX
) as the main system clock (f
MAIN
)
Notes 1. Bits 7 and 5 are read-only.
2.
Changing the value of the MCM0 bit is prohibited while the CSS bit is set to 1.
Cautions 1. Be sure to set bit 3 to 0 to 0.
2. The clock set by the CSS bit is supplied to the CPU and peripheral hardware. If the
CPU clock is changed, therefore, the clock supplied to peripheral hardware (except
the real-time clock, 12-bit interval timer, clock output/buzzer output, and watchdog
timer) is also changed at the same time. Consequently, stop each peripheral
function when changing the CPU/peripheral hardware clock.
3.
If the subsystem clock is used as the peripheral hardware clock, the operations of
the A/D converter and IICA are not guaranteed. For the operating characteristics of
the peripheral hardware, refer to the chapters describing the various peripheral
hardware as well as CHAPTER 29 ELECTRICAL SPECIFICATIONS (T
A
=
−40 to
+85
°C), CHAPTER 30 ELECTRICAL SPECIFICATIONS (G: INDUSTRIAL
APPLICATIONS T
A
=
−40 to + 105°C).
Remark f
IH
:
High-speed on-chip oscillator clock frequency
f
MX
:
High-speed system clock frequency
f
MAIN
:
Main system clock frequency
f
SUB
:
Subsystem clock frequency