7906 datasheet(450/531 Pages) RENESAS

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APPENDIX

7906 Group User’s Manual Rev.2.0

20-45

Appendix 4. Examples of handling unused pins

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

described below.

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

and properly evaluate their performance.

Table 1 Example of handling unused pins

Fig. 1 Example 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 (Note 1).

Connect this pin to Vcc via a resistor.

Select a falling edge for pin INT4.

Leave these pins open.

Connect this pin to Vcc.

Connect these pins to Vss.

Pin name

P1, P2, P5 to P7

P6OUTCUT/INT4

XOUT (Note 2), VCONT (Note 3)

AVCC

AVSS, VREF

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

these port pins are placed in the input mode 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 port pins are placed in the input 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.

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

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

3: Be sure that the PLL circuit operation enable bit (bit 1 at address BC16) = “0.”

P1, P2, P5 to P7

Left open

VCC

VSS

P1, P2, P5 to P7

AVCC

AVSS

VREF

XOUT

VCONT

AVCC

AVSS

VREF

XOUT

VCONT

VSS

VCC

P6OUTCUT/INT4

When setting port pins to input mode

When setting port pins to output mode

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