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PCI-1751U User Manual 16

Chapter 3 Installation

3.1 Operation

This chapter describes the operating characteristics of the PCI-1751U.

The driver software provided allows a user to access all of the card's func-

tions without register level programming. Please see the User's Manual

for the driver bundled with this card for more information. For users who

prefer to implement their own bit-level programming to drive the card's

functions, information useful for making such a program is included in

this chapter.

3.2 Digital I/O Ports

3.2.1 Introduction

The PCI-1751U emulates two 8255 programmable peripheral interface

(PPI) chips in mode 0, but with higher driving capability than a standard

8255 chip. Each of the 8255 chips has 24 programmable I/O pins that are

divided into three 8-bit ports. The total 48 DI/O pins from both chips are

divided into 6 ports, designated PA0, PB0, PC0, PA1, PB1 and PC1.

Each port can be programmed as an input or an output port. The I/O pins

in port A0 are designated PA00, PA01,..., PA07; the pins in port B0 are

designated PB00, PB01,..., PB07, etc. These port names are used both in

this manual and in the software library. Refer to Section 2.5, Pin Assign-

ments.

3.2.2 8255 Mode 0

The basic functions of 8255 mode 0 include:

• Two 8-bit I/O ports - port A (PA) and port B (PB)

• Port C is divided into two nibble-wide (4-bit) I/O ports:- PC upper and

PC lower

• Any port can be used for either input or output.

• Output status can be read back.

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