# Introduction to Bioinformatics - North South University

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4 Οκτ 2013 (πριν από 4 χρόνια και 9 μήνες)

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Lecture 13

Basic I/O Interface

Presented By

Dr.

Hosain

Asst. Prof. EECS, NSU

I/O port address decoding is very similar to

Any I/O device is addressed by a port number

or write to that port address

INS Instructions

INSB

Input String Byte, from I/O device to
memory location

Table 4
-
14: From
Brey’s

Book

Example

Read 50 bytes of data from an I/O device whose address in
03ACH and store the data in LISTS array

Example 4
-
7: From
Brey’s

Book

OUTS Instructions

OUTSB

Output String Byte, from string
memory location to I/O device

Table 4
-
15: From
Brey’s

Book

Example

Transfer data form memory array (ARRAY) to
an I/O device at I/O address 3ACH

Example 4
-
8: From
Brey’s

Book

Decoding 8
-

Decode 8
-
bit I/O ports F0H

F7H using 74ALS138 decoder

1111

0000 = F0H

1111 0111 = F7H

Decoding 8
-

Develop an I/O port decoder, using a 74ALS138, for the 8
-
bit I/O port
12H, 14H, 16H, 18H, 1AH, 1CH and 1EH

The Programmable Peripheral Interface (PPI)

82C55 is a very popular low
-
cost
interfacing component found in many
applications

It
sits between microprocessor and the
I/O devices

It has three ports

Port A

Port B

Port C

Also has an internal command register

Why Peripheral?

I/O Devices

Interfacing 82C55

Connect 82C55 so that it functions at 8
-
bit I/O port addresses C0H (port A), C2H
(port B), C4H (port C), and C6H (command register).

1100 0000 = C0H

1100

0010 = C2H

1100 0100 = C4H

1100 0110 = C6H

Interfacing 82C55

Draw the diagram for interfacing 82C55 for the following addresses 8C (Port A), 9C

(Port B), AC (Port C) and BC (command register).

CBA

011

References

Chapter 9 The Intel Microprocessors

by Barry B.
Brey