Operation Theorem
•
23
4.1.4 Digital I/O Port Programming
Users can write the digital output value to or read back the digital signal
level from the PPI ports by using the software library. Here we define the
port name in Table 4.1. These port names are used both in software library
and all through this manual. The programming for
PCIDIO 24H/48H
and
PCIDIO 96H are
fully compatible.
Connector
Numbers
CN1
CN2
CN3
CN4
P1A
P2A
P3A
P4A
Port
P1B
P2B
P3B
P4B
Names
P1C
P2C
P3C
P4C
P1CTRL
P2CTRL
P3CTRL
P4CTRL
Table 4.1 I/O Port Names
There are four ports on every 8255 PPI, including port A,B,C and the control
port. PA, PB and PC could be written or read but the control port is write
only. Refer to chapter 5 for details about programming of DIO ports.
4.1.5 Control Word
The control word written in the control port is used to setup PA, PB and PC
as input or output port. Figure 4.1 shows the format of the control word.
Table 4.2 shows the 16 possible control words and the respective I/O
configurations .
X X X ? ?
?
X
?
1/0 : Input/Output of Port C low nibble
D7 D6 D5 D4 D3 D2 D1 D0
1/0 : Input/Output of Port B
1/0 : Input/Output of Port C high nibble
1/0 : Input/Output of Port A
X : don't care
Figure 4.1 Control Word Format
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