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RL78/G1A CHAPTER 5 CLOCK GENERATOR
R01UH0305EJ0200 Rev.2.00 175
Jul 04, 2013
Table 5-5. Changing CPU Clock (2/2)
CPU Clock
Before Change After Change
Condition Before Change Processing After Change
High-speed on-
chip oscillator
clock
Oscillation of high-speed on-chip oscillator
and selection of high-speed on-chip
oscillator clock as main system clock
• HIOSTOP = 0, MCS = 0
X1 clock
Stabilization of X1 oscillation and selection
of high-speed system clock as main system
clock
• OSCSEL = 1, EXCLK = 0, MSTOP = 0
• After elapse of oscillation stabilization time
• MCS = 1
External main
system clock
Enabling input of external clock from the
EXCLK pin and selection of high-speed
system clock as main system clock
• OSCSEL = 1, EXCLK = 1, MSTOP = 0
• MCS = 1
XT1 oscillation can be stopped (XTSTOP =
1)
XT1 clock
External
subsystem clock
Transition not possible
−
High-speed on-
chip oscillator
clock
Oscillation of high-speed on-chip oscillator
and selection of high-speed on-chip
oscillator clock as main system clock
• HIOSTOP = 0, MCS = 0
X1 clock
Stabilization of X1 oscillation and selection
of high-speed system clock as main system
clock
• OSCSEL = 1, EXCLK = 0, MSTOP = 0
• After elapse of oscillation stabilization time
• MCS = 1
External main
system clock
Enabling input of external clock from the
EXCLK pin and selection of high-speed
system clock as main system clock
• OSCSEL = 1, EXCLK = 1, MSTOP = 0
• MCS = 1
External subsystem clock input can be
disabled (XTSTOP = 1).
External
subsystem clock
XT1 clock Transition not possible
−