4501 datasheet(203/212 Pages) RENESAS

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3.3 List of precautions

3-34

Rev.2.01

Feb 07, 2005

4501 Group

APPENDIX

REJ09B0192-0201

3.3.9 Notes on oscillation control

(1)

Clock control

Execute the CMCK or the CRCK instruction 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. Other 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 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 released

from reset, be careful that the variable frequency of the on-chip oscillator clock.

(3)

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 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.

3.3.10 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.

3.3.11 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.

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