
APPLICATION
2-39
4502 Group User’s Manual
2.5 Reset
System reset is performed by applying “L” level to the RESET pin for 1 machine cycle or more when the
following conditions are satisfied:
qthe value of supply voltage is the minimum value or more of the recommended operating conditions
qoscillation is stabilized.
Then when “H” level is applied to RESET pin, the software starts from address 0 in page 0 after elapsing
of the internal oscillation stabilizing time (Ring oscillator (internal oscillator) clock is counted for 5359 times).
Figure 2.5.2 shows the oscillation stabilizing time.
2.5.1 Reset circuit
The 4502 Group has the voltage drop detection circuit.
(1)
Power-on reset
Reset can be automatically performed at power on (power-on reset) by the built-in power-on reset
circuit. When the built-in power-on reset circuit is used, the time for the supply voltage to rise from
0 V to 2.0 V must be set to 100
s or less. If the rising time exceeds 100 s, connect a capacitor
between the RESET pin and VSS at the shortest distance, and input “L” level to RESET pin until the
value of supply voltage reaches the minimum operating voltage.
Fig. 2.5.1 Power-on reset circuit example
Fig. 2.5.2 Oscillation stabilizing time after system is released from reset
2.5 Reset
RESET pin
WEF
Watchdog reset signal
(Note 1)
Pull-up transistor
(Note 1)
Power-on reset circuit
Volgate drop detection circuit
VDD (Note 3)
100
s or less
(Note 2)
Internal reset signal
Power-on
Reset released
Internal reset signal
Reset
state
Notes 1:
This symbol represents a parasitic diode.
2: Applied potential to RESET pin must be VDD or less.
3: Keep the value of supply voltage to the minimum value
or more of the recommended operating conditions.
Power-on reset circuit output
RESET
0.3VDD
0.85VDD
(Note)
Note: Keep the value of supply voltage to the minimum value
or more of the recommended operating conditions.
Reset input
1 machine cycle or more
=
Program starts
(address 0 in page 0)
Ring oscillator (internal oscillator)
is counted 5359 times.