H8S2245 datasheet(3/818 Pages) RENESAS

3 / 818 page

Rev.3.00 Mar. 26, 2007 Page iii of xlii

REJ09B0355-0300

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 may occur due to the false recognition of the pin state as an input signal.

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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