
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
M37721
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
1
XOUT
Left open
V
P43–P47, P5–P10
M37721
VSS
HOLD
RDY
AVCC
CNVSS
AVSS
VREF
VCC
Left open
ST0
ST1
BLE
BHE
ALE
1
XOUT
Left open
V
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