455A Datasheet, PDF (51/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

455A Group
(1) RESET pin input
System reset is performed certainly by applying “L” level to
RESET pin for 1 machine cycle or more when the following
condition is satisfied;
the value of supply voltage is the minimum value or more of the
recommended operating conditions.
Reset input
1 machine cycle or more
RESET
0.3VDD
(Note 1)
0.85VDD
Program starts
(address 0 in page 0)
f(HSOCO)
High-speed on-chip oscillator (internal oscillator) is
counted 1376 times (Note 2).
Notes 1: Keep the value of supply voltage to the minimum value or more of the
recommended operating conditions.
2: It depends on the internal state at reset.
Fig 49. RESET pin input waveform and reset release timing
(2) 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, set the time for the supply voltage
to rise from 0 V to the minimum voltage of recommended
operating conditions to 100 µs or less.
If the rising time exceeds 100 µs, 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.
(3) System reset instruction (SRST)
By executing the SRST instruction, “L” level is output to RESET
pin and system reset is performed.
100µs or less
VDD (Note)
Power-on reset
circuit output
Internal reset signal
Power-on Reset Reset
state released
Note: Keep the value of supply voltage to
the minimum value or more of the
recommended operating conditions.
Fig 50. Power-on reset operation
Rev.1.01 Feb 15, 2008 Page 51 of 146
REJ03B0224-0101