38K2 datasheet(3/358 Pages) RENESAS

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General Precautions in the Handling of MPU/MCU Products

The following usage notes are applicable to all MPU/MCU products from Renesas. For detailed usage notes on the

products covered by this manual, refer to the relevant sections of the manual. If the descriptions under General

Precautions in the Handling of MPU/MCU Products and in the body of the manual differ from each other, the description

in the body of the manual takes precedence.

1. Handling of Unused Pins

Handle unused pins in accord with the directions given under Handling of Unused Pins in the manual.

 The input pins of CMOS products are generally in the high-impedance state. In operation with an

unused pin in the open-circuit state, extra electromagnetic noise is induced in the vicinity of LSI, an

associated shoot-through current flows internally, and malfunctions occur due to the false

recognition of the pin state as an input signal become possible. Unused pins should be handled as

described under Handling of Unused Pins in the manual.

2. Processing at Power-on

The state of the product is undefined at the moment when power is supplied.

 The states of internal circuits in the LSI are indeterminate and the states of register settings and pins

are undefined at the moment when power is supplied.

In a finished product where the reset signal is applied to the external reset pin, the states of pins are

not guaranteed from the moment when power is supplied until the reset process is completed.

In a similar way, the states of pins in a product that is reset by an on-chip power-on reset function

are not guaranteed from the moment when power is supplied until the power reaches the level at

which resetting has been specified.

3. Prohibition of Access to Reserved Addresses

Access to reserved addresses is prohibited.

 The reserved addresses are provided for the possible future expansion of functions. Do not access

these addresses; the correct operation of LSI is not guaranteed if they are accessed.

4. Clock Signals

After applying a reset, only release the reset line after the operating clock signal has become stable.

When switching the clock signal during program execution, wait until the target clock signal has

stabilized.

 When the clock signal is generated with an external resonator (or from an external oscillator) during

a reset, ensure that the reset line is only released after full stabilization of the clock signal. Moreover,

when switching to a clock signal produced with an external resonator (or by an external oscillator)

while program execution is in progress, wait until the target clock signal is stable.

5. Differences between Products

Before changing from one product to another, i.e. to one with a different type number, confirm that the

change will not lead to problems.

 The characteristics of MPU/MCU in the same group but having different type numbers may differ

because of the differences in internal memory capacity and layout pattern. When changing to

products of different type numbers, implement a system-evaluation test for each of the products.

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