Renesas RL78/G1P Hardware User Manual page 135

RL78/G1P
Figure 5-13. Clock Generator Operation When Power Supply Voltage Is Turned On
Lower limit of the operating voltage range
Power supply voltage (V
Power-on-reset
RESET pin
CPU clock
High-speed on-chip oscillator clock (f
High-speed system clock (f
(when X1 oscillation selected)
<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 27.4 AC Characteristics (the above figure is an
example when the external reset is in use).
<2> When the power supply voltage exceeds 1.51 V (TYP.), 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 a
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 set switching via
software (see 5.6.2 Example of setting X1 oscillation clock).
The internal reset processing time includes the oscillation accuracy stabilization time of the high-speed on-
Notes 1.
chip oscillator clock.
When releasing a reset, confirm the oscillation stabilization time for the X1 clock using the oscillation
2.
stabilization time counter status register (OSTC).
For the reset processing time, see CHAPTER 18 POWER-ON-RESET CIRCUIT.
3.
Caution It is not necessary to wait for the oscillation stabilization time when an external clock input from the
EXCLK pin is used.
R01UH0895EJ0100 Rev.1.00
Nov 29, 2019
10 μs or
more
)
DD
V
POR
0 V
<1>
Reset processing
time
<2>
)
IH
Note 1
)
MX
CHAPTER 5 CLOCK GENERATOR
Note 3
<3>
High-speed on-chip
oscillator clock
<4>
X1 clock oscillation
stabilization time
Switched by software
<5>
High-speed
system clock
Note 2
116