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Chapter 2 Pin Functions
2
2.3 I/O CIRCUITS AND UNUSED-PIN HANDLING

Table 2-4 lists the types of I/O circuits provided for each pin and describes how pins are handled when not used.

Fig. 2-1 illustrates the I/O circuit types.

Table 2-4 Types of I/O Circuits and Unused-Pin Handling

P00-P07
P20/NMI
P21/INTP0
P22/INTP1
P23/INTP2/CI
P24/INTP3
P25/INTP4/ASCK
P26/INTP5
P27/SI
P30/RxD
P31/TxD
P32/SCK
P33/SB0/SO
P34/TO0-P37/TO3
P40/AD0-P47/AD7
P50/A8-P57/A15
P60/A16-P63/A19
P64/RD
P65/WR
P66/WAIT/AN6
P67/REFRQ/AN7
P70/AN0-P75/AN5
ASTB
RESET
EA
AVREF
AVSS
Pin Input/output Recommended unused-pin handling
Leave open.
Type of I/O circuit
4 Output
2
5-A
8-A
10-A
2-A
5-A
4
5-A
11
9
4
2
1
Connect to VDD or VSS.
Connect to VDD.
Leave open.
Connect to VDD when used as an input pin.
Leave open when used as an output pin.
Connect to VDD when used as an input pin.
Leave open when used as an output pin.
Connect to VDDNote when used as an input pin.
Leave open when used as an output pin.
Connect to VSS.
Leave open.
Connect to VDD or VSSNote.
Connect to VSS.
Input
Input/output
Output
Input/output
Input
Output
Input
Note See Section 8.6.
Remark Since the type numbers of I/O circuits are numbered in the 78K series, they may not be serial in a certain product. (A product may
not contain some of these I/O circuits.)
Caution When an I/O pin is used as both an input and output pin, connect the pin to the VDD pin through a resistor of less than 100 kilohms.
(Especially, when the RESET pin goes to a voltage higher than the low level upon power on, or when an I/O pin is switched with
software.)