RL78/G15 CHAPTER 5 CLOCK GENERATOR
R01UH0959EJ0110 Rev.1.10 Page 151 of 765
Mar 7, 2023
Figure 5-13. Clock Generator Operation When Power Supply Voltage Is Turned On
High-speed on-chip
oscillator clock (
f
IH
)
CPU clock
________________
Internal reset signal
0
V
Power supply
voltage
(V
DD
)
<
1>
<
2>
<3>
<
4
>
<5>
SPOR reset
release voltage
High
-speed system
clock
(f
MX
) (when X1
oscillation selected
)
SPOR reset
processing
Note
3
High-
speed on
-chip oscillator clock
High
-speed system clock
Switched by
software
Note
1
X1 clock oscillation stabilization
time
Note 2
Starting X1 oscillation is
specified by software.
<1> When the power is turned on, an internal reset signal is generated by the selectable power-on-reset (SPOR)
circuit.
<2> When the power supply voltage exceeds detection voltage of the SPOR circuit, the reset is released and the
high-speed on-chip oscillator automatically starts oscillation.
<3> The CPU starts operation on the high-speed on-chip oscillator clock after waiting for the voltage to stabilize and
an SPOR reset processing have been performed after reset release.
<4> Set the start of oscillation of the X1 clock via software (see 5.6.2 Example of setting X1 oscillation clock).
<5> When switching the CPU clock to the X1 clock, wait for the clock oscillation to stabilize, and then switch the
clock via software.
Note 1. The reset processing time includes the oscillation accuracy stabilization time of the high-speed on-chip
oscillator clock.
Note 2. When releasing a reset, confirm the oscillation stabilization time for the X1 clock using the oscillation
stabilization time counter status register (OSTC).
Note 3. For SPOR reset processing time, see CHAPTER 17 SELECTABLE POWER-ON-RESET CIRCUIT.
Caution When an external clock input from the EXCLK pin is in use, oscillation stabilization time is
unnecessary.
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