Programming
5-3
To simplify your selection of a Control Byte to match your choice of port direc-
tions, use Table 5-1. This chart summarizes information from the Intel
Peripheral
Data
book on control words and their port directions for Mode 0.
When a port is programmed as an output, you can return the data that is present on
the output lines by reading the same location. Note that this reflects the actual state of
the output lines: if one or more is shorted, you are actually reading back the state of
the output lines.
Selecting an application programming interface
The PIO Series supports two different device driver interfaces to best match your
programming needs. The supported driver interfaces are:
•
DriverLINX
— An interface that is hardware and operating system indepen-
dent and supports multi-tasking, multi-threading applications.
•
Direct I/O
— An interface that is operating system independent and supports
single-tasking, single-threaded access to an Intel 8255-like function call
interface.
Table 5-1
Mode 0 control words and port directions
Control Byte
Port A
Port B
Port C
(0 - 3)
Port C
(4 - 7)
80h
81h
82h
83h
88h
89h
8Ah
8Bh
90h
91h
92h
93h
98h
99h
9Ah
9Bh
Out
Out
Out
Out
Out
Out
Out
Out
In
In
In
In
In
In
In
In
Out
Out
In
In
Out
Out
In
In
Out
Out
In
In
Out
Out
In
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
Out
Out
Out
In
In
In
In
Out
Out
Out
Out
In
In
In
In
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