M38262ECFS datasheet(74/91 Pages) RENESAS

74 / 91 page

Rev.1.00

Sep 06, 2006

page 74 of 88

REJ03B0181-0100

3826 Group (One Time PROM version)

3.3.3 Termination of unused pins

(1)

Terminate unused pins

Perform the following wiring at the shortest possible distance (20 mm or less) from microcomputer

pins.

➀Output ports

Open them.

➁Input ports

Connect each pin to VCC or VSS through each resistor of 1 kΩ to 10 kΩ.

A for pins whose potential affects to operation modes such as the INTi pin or others, select the

VCC pin or the VSS pin according to their operation mode.

➂ I/O ports

Set the I/O ports for the input mode and connect each pin to VCC or VSS through each resistor

of 1 kΩ to 10 kΩ. The port which can select a built-in pull-up resistor can also use the built-

in pull-up resistor.

When using the I/O ports as the output mode, open them at “L” or “H”.

• When opening them in the output mode, the input mode of the initial status remains until the

mode of the ports is switched over to the output mode by the program after reset. Thus, the

potential at these pins is undefined and the power source current may increase in the input

mode. With regard to an effects on the system, thoroughly perform system evaluation on the

user side.

• Since the direction register setup may be changed because of a program runaway or noise,

set direction registers by program periodically to increase the reliability of program.

(2)

Termination remarks

■ Input ports

Do not open them.

● Reason

• The power source current may increase depending on the first-stage circuit.

• An effect due to noise may be easily produced as compared with proper termination ➁

shown on the above.

■ I/0 ports setting as input mode

[1] Do not open in the input mode.

● Reason

• The power source current may increase depending on the first-stage circuit.

• An effect due to noise may be easily produced as compared with proper termination ➂

shown on the above.

[2] I/O ports :

Do not connect to VCC or VSS directly.

● Reason

If the direction register setup changes for the output mode because of a program runaway

or noise, a short circuit may occur.

[3] I/O ports :

Do not connect multiple ports in a lump to VCC or VSS through a resistor.

● Reason

If the direction register setup changes for the output mode because of a program runaway

or noise, a short circuit may occur between ports.

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