Renesas RL78/G1H, User Manual

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RL78/G1H CHAPTER 6 CLOCK GENERATOR
R01UH0575EJ0120 Rev. 1.20 Page 123 of 920
Dec 22, 2016
Figure 6 - 18 Clock Generator Operation When Power Supply Voltage Is Turned On
<1> When the power is turned on, an internal reset signal is generated by the power-on-reset (POR) circuit.
Note that the reset state is maintained after a reset by the voltage detection circuit or an external reset until the voltage reaches
the range of operating voltage described in
31.4 AC Characteristics (the above figure is an example when the external reset is
in use).
<2> When the reset is released, 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 a reset
processing have been performed after reset release.
<4> Set the start of oscillation of the X1 or XT1 clock via software (see 6.6.2 Example of setting X1 oscillation clock and 6.6.3
Example of setting XT1 oscillation clock ).
<5> When switching the CPU clock to the X1 or XT1 clock, wait for the clock oscillation to stabilize, and then set switching via
software (see 6.6.2 Example of setting X1 oscillation clock and 6.6.3 Example of setting XT1 oscillation clock ).
Note 1. The internal 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 the reset processing time, see CHAPTER 21 RESET FUNCTION .
Caution It is not necessary to wait for the oscillation stabilization time when an external clock input from the EXCLK pin
is used.
<2>
<3>
<4>
<5>
<5>
<4>
Note 1
Starting XT1 oscillation is specified by software.
Subsystem clock (f
SUB
)
(when XT1 oscillation
selected)
Starting X1 oscillation
is specified by software.
High-speed system clock
(f
MX
)
(when X1 oscillation
selected)
High-speed on-chip
oscillator clock (f
IH
)
CPU clock
Reset processing
time
Note 3
0 V
Power supply voltage (V
DD
)
V
POR
10 µs or
more
Lower limit of the operating
voltage range
Switched by software
High-speed on-chip
oscillator clock
High-speed
system clock
Subsystem clock
X1 clock oscillation
stabilization time
Note 2
RESET pin
<1>
Power-on-reset