7751 Datasheet, PDF (485/540 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER

APPENDIX
Appendix 5. Example for processing unused pins
Appendix 5. Example for processing unused pins
Table 1 Example for processing unused pins in single-chip mode
Pin name
Example of processing
Ports P0 to P8
Set for input mode and connect these pins to Vcc or
Vss via a resistor; or set for output mode and leave
these pins open. (Note 1)
_
E
Leave it open.
XOUT (Note 2)
AVcc
Connect this pin to Vcc.
AVss, VREF, BYTE
Connect these pins to Vss.
Notes 1: When setting these ports to the output mode and leave them open, they remain set to the input
mode until they are switched to the output mode by software after reset. While ports remain set
to the input mode, consequently, voltage levels of pins are unstable, and a power source current
can increase.
The contents of the direction register can be changed by noise or a program runaway generated
by noise. To improve its reliability, we recommend to periodically set the contents of the direction
register by software.
When processing unused pins, use the possible shortest wiring (within 20 mm from the microcomputer).
2: This applies when a clock externally generated is input to the XIN pin.
20–34
7751 Group User’s Manual