RL78/G1H CHAPTER 6 CLOCK GENERATOR
R01UH0575EJ0120 Rev. 1.20 Page 104 of 920
Dec 22, 2016
6.3.2 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 6 - 3 Format of System clock control register (CKC)
Note 1. Bits 7 and 5 are read-only.
Note 2. Changing the value of the MCM0 bit is prohibited while the CSS bit is set to 1.
Remark fIH: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
Caution 1. Be sure to set bits 0 to 3 of the CKC register to 0.
Caution 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.
Caution 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 31 ELECTRICAL
SPECIFICATIONS.
Address: FFFA4H After reset: 00H R/W
Note 1
Symbol<7><6><5><4>3210
CKCCLSCSSMCSMCM00000
CLS Status of CPU/peripheral hardware clock (f
CLK)
0 Main system clock (f
MAIN)
1 Subsystem clock (f
SUB)
CSS
Note 2
Selection of CPU/peripheral hardware clock (fCLK)
0 Main system clock (f
MAIN)
1 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 (fMAIN) operation control
0 Selects the high-speed on-chip oscillator clock (f
IH) as the main system clock (fMAIN)
1 Selects the high-speed system clock (f
MX) as the main system clock (fMAIN)
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