Advantech PCI-1751, User Manual

Page: 21 / 40

13 PCI-1751 User Manual
Chapter 3
S
ignal Connections
3.4 Digital I/O Ports
Introduction
The PCI-1751 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 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.

Output status can be read back.
Interrupt Function of the DIO Signals
Two I/O pins (PC00 and PC10) can be used to generate hardware interrupts. A user
can program the interrupt control register (Base + 32) to select the interrupt sources.
Refer to "Interrupt Function" in this chapter for details about interrupt control.
Input/Output Control
A control word can be written to a port's configuration register (Base+3 for port 0 and
Base+7 for port 1) to set the port as an input or an output port, unless the ports are
set as output ports via jumpers (refer to Section 2.3, Jumper Settings). Table 3-1
shows the format of a control word.
Table 3.3: Bit map of Port Configuration Register
D7 D6 D5 D4 D3 D2 D1 D0
Don’t care Don’t care Don’t care
Port A
0: output
1: input
Port C
higher bits
0: output
1: input
Don’t care
Port B
0: output
1: input
Port C
lower bits
0: output
1: input
Note!
A control word has no effect if the corresponding port is set as an output
port by a jumper.
Warning!
Before setting any port as an output port via software, make sure that a
safe output value has also been set. An output voltage will appear at the
pins immediately following the control word taking effect.
If no output value was specified, the value will be indeterminate (either 0
or 1), which may cause a dangerous condition.