7721 datasheet(504/577 Pages) RENESAS

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APPENDIX

7721 Group User’s Manual

17–41

Appendix 5. Examples of handling unused pins

Examples of handling unused pins are described below. These descriptions are just examples. The user

shall modify them according to the actual application and test them.

Table 1 Examples of handling unused pins

Handling example

Connect these pins to the Vcc or Vss pin via resistors

after these pins are set to the input mode, or leave

these pins open after they are set to the output mode

(Notes 1, 2).

Leave this pin open.

Connect these pins to the Vcc pin via resistors (These

pins are pulled high.) (Note 2)

Connect this pin to the Vcc pin or Vss pin.

Connect this pin to the Vcc pin.

Connect these pins to the Vss pin.

Pins

P43 to P47, P5 to P10

____

BLE, BHE, ALE,

φ1, ST0, ST1

XOUT (Note 3)

_____

____

HOLD, RDY

CNVss

AVcc

AVss, VREF

P43–P47, P5–P10

VSS

HOLD

RDY

AVCC

CNVSS

AVSS

VREF

VCC

Left open

q When setting ports to input mode

q When setting ports to output mode

ST0

ST1

BLE

BHE

ALE

XOUT

Left open

P43–P47, P5–P10

VSS

HOLD

RDY

AVCC

CNVSS

AVSS

VREF

VCC

Left open

ST0

ST1

BLE

BHE

ALE

XOUT

Left open

V CNVss pin can be connected to Vcc pin.

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. Accordingly, set these ports to the output mode immediately after

reset. Software reliability can be enhanced when the contents of the above ports’ direction registers

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

which occurs 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.

Fig. 2 Examples of handling unused pins

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