
7721 Group User’s Manual
6–7
INPUT/OUTPUT PINS
6.3 Examples of handling unused pins
When unusing an I/O pin, some handling is necessary for the pin. Examples of handling unused pins are
described below.
The following are just examples. The user shall modify them according to the user’s actual application and
test them.
Table 6.3.1 Examples of handling unused pins
6.3 Examples 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 (Notes 1 and 2).
Leave them open.
Connect these pins to Vcc via a resistor (pull-up) (Note 2).
Connect this pin to Vcc or Vss.
Connect this pin to Vcc.
Connect these pins to Vss.
Pin name
P43 to P47, P5 to P10
___
BLE, BHE, ALE,
φ1, ST0, ST1
XOUT (Note 3)
_____
____
HOLD, RDY
CNVss
AVcc
AVss, VREF
Fig. 6.3.1 Examples of handling unused pins
P43–P47, P5–P10
M37721
ST0
ST1
BLE
BHE
ALE
1
XOUT
AVSS
VREF
HOLD
RDY
M37721
VCC
VSS
AVCC
q When setting ports to input mode
q When setting ports to output mode
Left open
AVSS
VREF
HOLD
RDY
VCC
VSS
AVCC
Left open
P43–P47, P5–P10
Left open
ST0
ST1
BLE
BHE
ALE
1
XOUT
CNVSSV
V CNVSS can be connected to VCC, too.
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. After reset, immediately set these ports to the output 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.
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.