4524_M Datasheet, PDF (301/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 Group
APPENDIX
3.3 List of precautions
3.3.12 Notes on oscillation circuit
(1) Clock control
Execute the CMCK or the CRCK instruction to select the main clock (f(XIN)) in the initial setting
routine of program (executing it in address 0 in page 0 is recommended).
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 instructions is valid. Another oscillation
circuits and the on-chip oscillator stop.
(2) On-chip oscillator
The clock frequency of the on-chip oscillator depends on the supply voltage and the operation
temperature range.
Be careful that margin of 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 released
from reset, be careful that the margin of frequencies of the on-chip oscillator clock.
(3) External clock
When the external clock signal is used as the main clock (f(XIN)), note that the power down mode
(POF or POF2 instructions) cannot be used.
(4) Value of a part connected to an oscillator
Values of a capacitor and a resistor of the oscillation circuit depend on the connected oscillator and
the board. Accordingly, consult the oscillator manufacturer for values of each part connected the
oscillator.
3.3.13 Electric characteristic differences between Mask ROM and One Time PROM version MCU
There are differences in electric characteristics, operation margin, 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 version, please perform sufficient evaluations for the commercial samples of the Mask ROM
version.
3.3.14 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.2.00 Aug, 06 2004
REJ09B0107-0200Z
3-47