4518 Datasheet, PDF (61/160 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4518 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.
VDCE
–
VRST ⁺
VRST ^-
+
Voltage drop detection circuit
Fig. 51 Voltage drop detection reset circuit
VDD
VRST+(reset release voltage)
VRST ^-(reset voltage)
Voltage drop detection circuit
Reset signal
RESET pin
Voltage drop detection circuit
Reset signal
Microcomupter starts operation after
on-chip oscillator (internal oscillator)
clock is counted 120 to 144 times.
Note: Detection voltage hysteresis of voltage drop detection circuit is 0.2 V (Typ).
Fig. 52 Voltage drop detection circuit operation waveform
Table 17 Voltage drop detection circuit operation state
VDCE pin
“L”
“H”
At CPU operating
Invalid
Valid
At RAM back-up
Invalid
Valid
Rev.3.01 2005.06.15 page 61 of 157
REJ03B0008-0301