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C-4
Control words that match various port directions are listed in Table C-3.
This table summarizes information from the Intel peripheral data book on
control words and their port directions for mode 0.
Control Word
80h
81h
82h
83h
88h
89h
8Ah
8Bh
90h
91h
92h
93h
98h
99h
9Ah
9Bh
All port registers of the 8255 PPI are cleared by a write to the control
register.
Table C-3. PIO Control Word
Port A
Port B
Out
Out
Out
Out
Out
In
Out
In
Out
Out
Out
Out
Out
In
Out
In
In
Out
In
Out
In
In
In
In
In
Out
In
Out
In
In
In
In
Port C
Port C
Lower 0 to 3
Upper 4 to 7
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Register Maps
Out
Out
Out
Out
In
In
In
In
Out
Out
Out
Out
In
In
In
In
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Troubleshooting
