![](http://datasheet.mmic.net.cn/Renesas-Electronics-America/UPD78F0394GC-8EA-A_datasheet_99854/UPD78F0394GC-8EA-A_139.png)
CHAPTER 6 CLOCK GENERATOR
User’s Manual U17473EJ2V0UD
137
Cautions 1. If the voltage rises with a slope of less than 0.5 V/ms (MIN.) from power application until the
voltage reaches 1.8 V, input a low level to the RESET pin from power application until the
voltage reaches 1.8 V, or set the 2.7 V/1.59 V POC mode by using the option byte (POCMODE
= 1) (see Figure 6-13).
By doing so, the CPU operates with the same timing as <2> and
thereafter in Figure 6-12 after reset release by the RESET pin.
2. It is not necessary to wait for the oscillation stabilization time when an external clock input
from the EXCLK and EXCLKS pins is used.
Remark While the microcontroller is operating, a clock that is not used as the CPU clock can be stopped via
software settings.
The internal high-speed oscillation clock and high-speed system clock can be
stopped by executing the STOP instruction (see (4) in 6.6.1
Example of controlling high-speed
system clock, (3) in 6.6.2 Example of controlling internal high-speed oscillation clock, and (4) in
6.6.3 Example of controlling subsystem clock).
Figure 6-13. Clock Generator Operation When Power Supply Voltage Is Turned On
(When 2.7 V/1.59 V POC Mode Is Set (Option Byte: POCMODE = 1))
Internal high-speed
oscillation clock (fRH)
CPU clock
High-speed
system clock (fXH)
(when X1 oscillation
selected)
Internal high-speed
oscillation clock
High-speed system clock
Switched by
software
Subsystem clock (fSUB)
(when XT1 oscillation
selected)
Subsystem clock
X1 clock
oscillation stabilization time:
2
11/fX to 216/fXNote
Starting X1 oscillation
is set by software.
Starting XT1 oscillation
is set by software.
Waiting for oscillation accuracy
stabilization (86 to 361 s)
Internal reset signal
0 V
2.7 V (TYP.)
Power supply
voltage (VDD)
<1>
<3>
<2>
<4>
<5>
Reset processing
(11 to 45 s)
<4>
<5>
μ
<1>
When the power is turned on, an internal reset signal is generated by the power-on-clear (POC) circuit.
<2> When the power supply voltage exceeds 2.7 V (TYP.), the reset is released and the internal high-speed
oscillator automatically starts oscillation.
<3> After the reset is released and reset processing is performed, the CPU starts operation on the internal high-
speed oscillation clock.
<4> Set the start of oscillation of the X1 or XT1 clock via software (see (1) in 6.6.1 Example of controlling high-
speed system clock and (1) in 6.6.3 Example of controlling subsystem 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 (3) in 6.6.1 Example of controlling high-speed system clock and (3) in 6.6.3
Example of controlling subsystem clock).
<R>