4524_M Datasheet, PDF (239/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 Group
APPLICATION
2.8 Voltage drop detection circuit
2.8 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 2.8.1 shows the voltage drop detection circuit, and Figure 2.8.2 shows the operation waveform example
of the voltage drop detection circuit. Table 2.8.1 shows the voltage drop detection circuit operation state.
Refer to section “3.1 Electrical characteristics” for the reset voltage of the voltage drop detection circuit.
S
QR
QS
R
EPOF instruction +POF instruction
EPOF instruction +POF2 instruction
Internal reset signal
T5F flag
Key-on wakeup signal
SVDE instruction
Internal reset signal
VDCE
–
VRST +
Voltage drop detection circuit
Reset signal
Voltage drop detection circuit
Fig. 2.8.1 Voltage drop detection circuit
VDD
VRST (detection
voltage)
Voltage drop detection circuit
Reset signal
RESET pin
Microcomupter starts operation after
on-chip oscillator (internal oscillator)
clock is counted 5400 to 5424 times.
Note: Detection voltage of voltage drop detection circuit does not have hysteresis.
Fig. 2.8.2 Voltage drop detection circuit operation waveform example
Table 2.8.1 Voltage drop detection circuit operation state
VDCE pin At CPU operating
At power down
(SVDE instruction is not executed)
“L”
Invalid
Invalid
“H”
Valid
Invalid
At power down
(SVDE instruction is executed)
Invalid
Valid
Rev.2.00 Aug, 06 2004
REJ09B0107-0200Z
2-75