7480 Group and 7481 Group User's Manual
1-38
HARDWARE
1.10 Input/Output Pins
1.10.4 Termination of Unused Pins
Table 1.10.1 lists the termination of unused pins.
Table 1.10.1 Termination of Unused Pins
Open
O (Note 2)
O (Note 5)
O (Note 2)
×
O (Note 5)
×
O
Termination
Connect to
VSS
×
O (Note 6)
×
O
×
Notes 1: Do not connect several pins of programmable I/O ports together to VCC or VSS through a resistor.
2: Every pin that is allowed to be open when unused has a special circuit structure which prevents
currents from flowing into the circuit unless the input to read signal is performed internally, even
if an intermediate level input is applied to the pin.
3: When these pins are pulled high, set the corresponding bits of port direction registers, port
registers and port P4P5 input control register so that each pin is in the input mode or output is
HIGH.
4: When these pins are pulled low, set the corresponding bits of port direction registers, pull-up
control registers, port registers so that each pin can be set to the input mode without pull-up
transistor or in the output is LOW.
5: Set these pins to the output mode and keep them open.
However, these I/O pins retain the input mode until the pins are switched to the output mode by
software after the microcomputer is released from reset. Therefore, the power source current may
increase depending on the input level of each pin.
Since their port direction registers might be switched into the input mode by program runaway or
noise, periodically set the port direction registers to the output mode by software.
6: A short wire can be used to directly connect any unused pin to the VCC or VSS pin without a
resistor, but a long wire must connect it through a resistor. Since the P33 pin of the built-in PROM
version has the alternative function of the VPP pin, connect the P33 pin to VCC or VSS with the
shortest wire through a resistor (about 5 k
), in series.
7: When these pins are pulled low, set the corresponding bits of port direction registers, port
registers and port P4P5 input control register so that each pin is in the input mode or output is
LOW.
8: The 7480 Group does not have port pins P24–P27, P42, P43, and P50–P53.
9: The AVSS pin is dedicated to the 44P6N-A package products in the 7481 Group.
Port
P0
P10–P13
P15, P17
P14, P16
P2 (Note 8)
P3
P4, P5
(Note 8)
AVSS (Note 9)
VREF
XOUT
Connect to
VCC
×
O (Note 6)
×
O
×
Pull-down to VSS through
a resistor (Note 1)
O (Note 4)
O (Note 6)
O (Note 7)
×
Pull-up to VCC through
a resistor (Note 1)
O (Note 3)
O (Note 6)
O (Note 3)
×