HD6433682 ETC, HD6433682 Datasheet - Page 375

• Manufacturer Part Number: HD6433682
• Description: Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series
• Manufacturer: ETC

20.3
20.3.1
Figure 20.2 shows the timing of the operation of the power-on reset circuit. As the power-supply
voltage rises, the capacitor which is externally connected to the RES pin is gradually charged via
the on-chip pull-up resistor (typ. 150 k ). Since the state of the RES pin is transmitted within the
chip, the prescaler S and the entire chip are in their reset states. When the level on the RES pin
reaches the specified value, the prescaler S is released from its reset state and it starts counting.
The OVF signal is generated to release the internal reset signal after the prescaler S has counted
131,072 clock ( ) cycles. The noise cancellation circuit of approximately 100 ns is incorporated to
prevent the incorrect operation of the chip by noise on the RES pin.
To achieve stable operation of this LSI, the power supply needs to rise to its full level and settles
within the specified time. The maximum time required for the power supply to rise and settle after
power has been supplied (t
which is connected to RES pin (C
supply voltage, the power supply circuit should be designed to satisfy the following formula.
Note that the power supply voltage (Vcc) must fall below Vpor = 100 mV and rise after charge on
the RES pin is removed. To remove charge on the RES pin, it is recommended that the diode
should be placed near Vcc. If the power supply voltage (Vcc) rises from the point above Vpor, a
power-on reset may not occur.
Vcc
PSS-reset
signal
OVF
Internal reset
signal
Power-On Reset Circuit
t
PWON
Operation
Vpor
(t
PWON
(ms)
t
PWON
Figure 20.2 Operational Timing of Power-On Reset Circuit
PSS counter starts
90
3000 ms, C
PWON
C
RES
131,072 cycles
) is determined by the oscillation frequency (f
( F)
RES
RES
). If t
162/f
0.22 F, and f
Reset released
PWON
OSC
means the time required to reach 90
(MHz)
OSC
= 10 in 2-MHz to 10-MHz operation)
Rev. 3.00, 05/03, page 345 of 472
OSC
) and capacitance
of power
Vss
Vss