4502 datasheet(159/214 Pages) RENESAS

159 / 214 page

2-42

Rev.2.01

Feb 02, 2005

4502 Group

APPLICATION

REJ09B0193-0201

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.

Fig. 2.6.1 Voltage drop detection circuit

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.

–

VRST

VDD

Reset signal

Return input

EPOF instruction + POF2 instruction

(continuous execution)

(Note 2)

Voltage drop detection circuit

reset signal

(Note 1)

Voltage drop detection circuit

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.

VDD

The microcomputer starts

operation after the on-chip

oscillator (internal oscillator)

is counted 5359 times.

Note 3

Voltage drop detection

circuit reset signal

RESET pin

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.

VRST

(Detection voltage)

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