38K2 datasheet(156/358 Pages) RENESAS

156 / 358 page

2.1 I/O port

Rev.2.00

Oct 15, 2006

page 7 of 112

38K2 Group

REJ09B0338-0200

APPLICATION

2.1.5 Termination of unused pins

(1)

Terminate unused pins

➀ I/O ports :

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

1 k

Ω to 10 kΩ. With regard to ports which can select the built-in pull-up resistor, the built-in pull-

up resistor can be used.

Set the I/O ports for the output mode and 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

➀ I/O ports :

Do not open in the input mode.

q 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 shown

in (1).

➁ I/O ports :

When setting for the input mode, do not connect to VCC or VSS directly.

q Reason

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

noise, a short circuit may occur between a port and VCC (or VSS).

➂ I/O ports :

When setting for the input mode, do not connect multiple ports in a lump to VCC or VSS through

a resistor.

q 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.

• At the termination of unused pins, perform wiring at the shortest possible distance (20 mm or less)

from microcomputer pins.

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