Specifications

Chapter 3 Function Description 17
3.1 Overview
This chapter describes the operating characteristics of the PCI-1757UP.
The driver software provided allows a user to access all of the card's
functions 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
Introduction
The PCI-1757UP emulates one 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, designated PA, PB and PC. Each port
can be programmed as an input or an output port. The I/O pins in port A
are designated PA0, PA1,..., PA7; the pins in port B are designated PB0,
PB1,..., PB7, etc. These port names are used both in this manual and in
the software library. Refer to Section 2.4, Pin Assignments.
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.