7721 datasheet(96/577 Pages) RENESAS

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7721 Group User’s Manual

6–7

INPUT/OUTPUT PINS

6.3 Examples of handling unused pins

When unusing an I/O pin, some handling is necessary for the pin. Examples of handling unused pins are

described below.

The following are just examples. The user shall modify them according to the user’s actual application and

test them.

Table 6.3.1 Examples of handling unused pins

6.3 Examples of handling unused pins

Handling example

Set these pins to the input mode and connect each

pin to Vcc or Vss via a resistor; or set these pins to

the output mode and leave them open (Notes 1 and 2).

Leave them open.

Connect these pins to Vcc via a resistor (pull-up) (Note 2).

Connect this pin to Vcc or Vss.

Connect this pin to Vcc.

Connect these pins to Vss.

Pin name

P43 to P47, P5 to P10

___

BLE, BHE, ALE,

φ1, ST0, ST1

XOUT (Note 3)

_____

____

HOLD, RDY

CNVss

AVcc

AVss, VREF

Fig. 6.3.1 Examples of handling unused pins

P43–P47, P5–P10

ST0

ST1

BLE

BHE

ALE

XOUT

AVSS

VREF

HOLD

RDY

VCC

VSS

AVCC

q When setting ports to input mode

q When setting ports to output mode

Left open

AVSS

VREF

HOLD

RDY

VCC

VSS

AVCC

Left open

P43–P47, P5–P10

Left open

ST0

ST1

BLE

BHE

ALE

XOUT

CNVSSV

V CNVSS can be connected to VCC, too.

Notes 1: When leaving these pins open after they are set to the output mode, note the following: these pins

function as input ports from reset until they are switched to the output mode by software. Therefore,

voltage levels of these pins are undefined and the power source current may increase while these

pins function as input ports. After reset, immediately set these ports to the output mode.

Software reliability can be enhanced by setting the contents of the above ports’ direction registers

periodically. This is because these contents may be changed by noise, a program runaway which

occurs owing to noise, etc.

2: For unused pins, use the shortest possible wiring (within 20 mm from the microcomputer’s pins).

3: This applies when a clock externally generated is input to the XIN pin.

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