INPUT/OUTPUT PINS
7902 Group User’s Manual
6-9
6.3 Examples of handling unused pins
6.3.2 In memory expansion and microprocessor modes
Table 6.3.2 Example of handling unused pins in memory expansion and microprocessor modes
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 2).
Set these pins to the input mode and leave them open (Notes 3,4)
Leave these pins open.
Connect this pin to Vcc.
Connect these pins to Vss.
Leave these pins open.
Connect these pins to Vcc via a resistor.
Pin name
P2 (Note 1), P30, P33 (Note 1), P40 to P43, P5 to P8
P44 to P47
NMI (Notes 3, 5), XOUT (Note 6), VCONT (Note 7)
AVCC
AVSS, VREF
φ1 (Note 8), ALE (Note 8), HLDA (Note 8)
RDY (Note 8), HOLD (Note 8)
Notes 1: This applies when the VCC level voltage is applied to pin BYTE.
2: 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 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.
3: Do not connect these pins to Vss.
4: Be sure that the pins P44–P47 pullup select bit (bit 4 at address 9216) = 0.
5: Be sure that the pin NMI pullup select bit (bit 7 at address 9216) = 0.
6: This applies when a clock externally generated is input to pin XIN.
7: Be sure that the PLL circuit operation enable bit (bit 1 at address BC16) = 0.
8: This applies when the Vcc-level voltage is applied to pin MD0. (It is also possible to disable these functions
by software and use these pins as programmable I/O port pins.)
Fig. 6.3.2 Example of handling unused pins in memory expansion and microprocessor modes
P2, P30, P33,
P40–P43, P5–P8
M37902
VCC
P44–P47
NMI
XOUT
VCONT
VCC
VSS
P2, P30, P33, P4–P8
M37902
AVCC
AVSS
VREF
AVCC
AVSS
VREF
VSS
φ1
ALE
HLDA
RDY
HOLD
VCC
φ1
ALE
HLDA
RDY
HOLD
NMI
XOUT
VCONT
VCC
When setting port pins to input mode
When setting port pins to output mode
Note: Be sure to set P44–P47 to the input mode.
Left open