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

CN1

CN2

CN3

CN4

Numbers

 

 

 

 

 

 

 

 

 

 

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 .

D7 D6 D5 D4 D3 D2 D1 D0

X X X ? ? X ? ?

1/0 : Input/Output of Port C low nibble

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

Operation Theorem ∙ 23