7902 Group User’s Manual
21-44
Appendix 4. Examples of handling unused pins
APPENDIX
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.
1. In the single-chip mode
Table 1 Example of handling unused pins in single-chip mode
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).
Set these pins to the input mode and leave them open (Notes 2, 3)
Leave these pins open.
Connect this pin to Vcc.
Connect these pins to Vss.
Pin name
P0 to P3, P40 to P43, P5 to P8, P10, P11
P44 to P47
NMI (Notes 2, 4), XOUT (Note 5), VCONT (Note 6)
AVCC
AVSS, VREF, BYTE
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: Do not connect these pins to Vss.
3: Be sure that the pins P44–P47 pullup select bit (bit 4 at address 9216) = 0.
4: Be sure that the pin NMI pullup select bit (bit 7 at address 9216) = 0.
5: This applies when a clock externally generated is input to pin XIN.
6: Be sure that the PLL circuit operation enable bit (bit 1 at address BC16) = 0.
Fig. 1 Example of handling unused pins in single-chip mode
P0–P3, P40–P43,
P5–P8, P10, P11
M37902
Left open
When setting port pins to input mode
VCC
P44–P47
NMI
XOUT
VCONT
VCC
VSS
P0–P8, P10, P11
M37902
When setting port pins to output mode (Note)
AVCC
AVSS
VREF
BYTE
AVCC
AVSS
VREF
BYTE
NMI
XOUT
VCONT
Note: Be sure to set P44–P47 to the input mode.
VSS
Left open