4501_M Datasheet, PDF (158/212 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4501 Group
APPLICATION
2.6 Voltage drop detection circuit
2.6 Voltage drop detection circuit
The built-in voltage drop detection circuit is designed to detect a drop in voltage and to reset the microcomputer
if the supply voltage drops below a set value.
Figure 2.6.1 shows the voltage drop detection circuit, and Figure 2.6.2 shows the operation waveform
example of the voltage drop detection circuit.
VDD
–
VRST +
(Note 2)
Voltage drop detection circuit
QS
R
(Note 1)
EPOF instruction +POF2 instruction
(continuous execution)
Reset signal
Return input
Voltage drop detection circuit
reset signal
Notes 1: In the RAM back-up mode by the POF2 instruction,
the voltage drop detection circuit stops.
2: When the VDD (supply voltage) is VRST (detection voltage) or less,
the voltage drop detection circuit reset signal is output.
Fig. 2.6.1 Voltage drop detection circuit
VDD
VRST
(detection voltage)
Voltage drop detection
circuit reset signal
RESET pin
Note 3
The microcomputer starts
operation after the on-chip
oscillator (internal oscillator)
is counted 5359 times.
Notes 1: After system is released from reset, the on-chip oscillator (internal oscillator)
is selected as the operation clock of the microcomputer.
2: Refer to the voltage drop detection circuit characteristics in the electrical characteristics
for the rating value of VRST (detection voltage).
3: The VRST (detection voltage) does not include hysteresis.
Fig. 2.6.2 Voltage drop detection circuit operation waveform example
Note: Refer to section “3.1 Electrical characteristics” for the reset voltage of the voltage drop detection
circuit.
Rev.2.01 Feb 07, 2005
REJ09B0192-0201
2-41