Computer Peripherals 02 .pdf

Communication Ports
LECTURE 02:PARALLEL PORTS

Communication Ports
INTRODUCTION

 There are two basic data transmission methods modern computes employ:

parallel data transmission and serial data transmission. In a serial data
transmission scheme one device sends data to another a single bit at a time
across one wire. In a parallel transmission scheme, one device sends data
to another several bits at a time (in parallel) on several different wires.

01010100100011111010101011001010101010101010
Serial transmission
Parallel port

0
1
1
0
1
1
0
1

Parallel transmission

2

Communication Ports

3

Communication Ports
PARALLEL PORTS

4

UNDERSTANDING THE PARALLEL PORT

Understanding the Parallel Port
Data Lines (D) used for output

13 12 11 10 9

8

7

6

5

4

3

2

1

25 24 23 22 21 20 19 18 17 16 15 14

Grounds
Status Lines (S) used for
input.

Control Lines (C) may be used
for input / output

Parallel Port - Output
Data Lines (D) used for output

13

25

12

24

11

23

10

22

D7

D6

D5

D4

D3

D2

D1

D0

9

8

7

6

5

4

3

2

21

20

19

18

17

16

15

14

Ground

1

Parallel Port - Output

D7

D6

D5

D4

D3

D2

D1

D0

128

64

32

16

8

4

2

1

27

26

25

24

23

22

21

20

Parallel Port
MODES OF OPERATIONS

 Compatibility Mode: "Centronics" or standard mode




It is commonly called the "Centronics" mode and is the method utilized with the
SPP (Standard Parallel Port).
This mode defines the protocol used by most PCs to transfer data to a printer.

 Nibble Mode:.


Transfers 4 bits at a time (a nibble) using Status Lines for data.

 Byte Mode: 8 bits at a time using data lines.


Added the capability to disable the drivers used for driving the data lines, and
allowed the data port to become an input read data port.

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