4502 Datasheet, PDF (51/116 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4502 Group
19 _{Power-on reset}
Reset can be automatically performed at power on (power-on re-
set) 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 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 RE-
SET pin until the value of supply voltage reaches the minimum
operating voltage.
20 _{Clock control}
Execute the CMCK or the CRCK instruction in the initial setting
routine of program (executing it in addres 0 in page 0 is recom-
mended).
The oscillation circuit by the CMCK or CRCK instruction can be
selected only at once. The oscillation circuit corresponding to the
first executed one of these two instruction is valid. Other oscilla-
tion circuits and the on-chip oscillator stop.
21 _{On-chip oscillator}
The clock frequency of the on-chip oscillator depends on the sup-
ply voltage and the operation temperature range.
Be careful that variable frequencies when designing application
products.
Also, the oscillation stabilize wait time after system is released
from reset is generated by the on-chip oscillator clock. When
considering the oscillation stabilize wait time after system is re-
leased from reset, be careful that the variable frequency of the
on-chip oscillator clock.
22 _{External clock}
When the external signal clock is used as the source oscillation
(f(XIN)), note that the RAM back-up mode (POF and POF2 in-
structions) cannot be used.
23 _{Electric Characteristic Differences Between Mask ROM and One}
Time PROM Version MCU
There are differences in electric characteristics, operation mar-
gin, noise immunity, and noise radiation between Mask ROM and
One Time PROM version MCUs due to the difference in the
manufacturing processes.
When manufacturing an application system with the One time
PROM version and then switching to use of the Mask ROM ver-
sion, please perform sufficient evaluations for the commercial
samples of the Mask ROM version.
24 _{Note on Power Source Voltage}
When the power source voltage value of a microcomputer is less
than the value which is indicated as the recommended operating
conditions, the microcomputer does not operate normally and
may perform unstable operation.
In a system where the power source voltage drops slowly when
the power source voltage drops or the power supply is turned off,
reset a microcomputer when the supply voltage is less than the
recommended operating conditions and design a system not to
cause errors to the system by this unstable operation.
Rev.3.01 2005.02.02 page 51 of 112
REJ03B0105-0301