4502 Datasheet, PDF (39/116 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4502 Group
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.
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. 37 Voltage drop detection circuit
VDD
Note 3
Voltage drop detection
circuit reset signal
RESET pin
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. 38 Voltage drop detection circuit operation waveform example
Rev.3.01 2005.02.02 page 39 of 112
REJ03B0105-0301