CHAPTER CHAPTER

Serial and Parallel Serial and Parallel CommunicationCommunication

Chapter Objectives

• Explain serial communication– Standards, ports, resources etc.

• Show a few examples of serial communication connections used in practice

• Describe the features of parallel communication– Standards, use etc.

Chapter Modules

• Serial communication• Newer serial communication

technologies• Serial communication connections• Parallel communication

Module

Serial Communication

Chapter Objectives

• Explain serial communication– Standards, ports, resources etc.

• Show a few examples of serial communication connections and ports used in practice

Definition of Serial Communication

Bit by bit transmission of information in seriesA B

Travels in series

Serial Communication Implementation

• Popular implementation found in older and some newer computers is known as the RS-232 serial connection found in microcomputers

• Newer type of serial connections– Universal Serial Bus (USB)– IEEE 1394 serial connection that is also

known as the FireWire connection

Other Serial Communication Technologies

• eSATA• Fiber channel

RS-232C Serial Standard• The most popular standard• Conforming serial ports are found in the

following – Micro– Minis and mainframes

• Sometimes these ports are also known as the asynchronous ports or asnch ports in short

• It is also possible to conduct synchronous transmission through these ports as well

Purpose of the Serial Ports

Parallel DigitalData

Serial Digital Data

OutIn

Expansion Bus

Seri

al In

terf

ace

Standard Serial Port on a Computer (DB 9)

Serial Port Identification

Source: Black Box

Male and Female Connectors

Pins Holes

Typical serial port

Typical parallel port

Source Black Box

Differentiating Between Serial and Parallel Ports

Serial Male Port

Parallel FemalePort

Serial Cable

DB25 Connector

DB9 Connector

Source Black Box

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Module

Resources for Serial Ports

Support for Serial Ports

• Both hardware and software support are required for the functioning of serial ports

• A microcomputer is supplied with two standard serial ports– Additional ports can be installed

Operating System Support

• Earlier operating systems– Supported four serial ports

• Today’s operating systems– Support a larger number of serial ports

• For most practical purposes, four serial ports are considered sufficient in a microcomputer– Only two, namely com1 and com2, are in

widespread use

Port Properties

Com 1

Com2

Com3

Com4

•IRQ

•I/O Address

•Base Memory Address

•Direct Memory Address (DMA) Channel

Assignment of Values

• The assignment of the respective values for each port must be unique

• An IRQ, I/O address or DMA conflict can lead to a disruption in the execution of an application– This is no more a problem with newer

OS and hardware

IRQ and Address Assignment

PORT IRQ ADDRESS------------------------------------------------------------

1 4 3F8-3FF

2 3 2F8-2FF

3

4

These values shouldnot normally bechanged.

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Module

Faster RS-232 Serial Ports and Summary

Older and Newer Serial Ports

• Older serial ports operated at a slower speed

• The newer serial ports operate at a faster speed

• The newer serial ports are equipped with a new processor

• The hardware in question is known as the UART processor

Enhanced Serial Ports

UART16550/16650

Com.Port

The newer processor is required for communication at speeds of 115,200 bps

Universal Asynchronous Receiver Transmitter (UART)

ISDN Line Requirement

• In theory, the maximum speed over a single ISDN line is approximately 128K bps

• If necessary, enhanced serial ports can be installed by installing a board containing the enhanced ports

UART-based Ports

In Summary• Two standard serial ports are present

on a microcomputer• Resources

– IRQ, I/O Address and DMA

• Port settings– Communication speed, length of the

data bits etc.

• Later versions of the UART chip are required to support high speed communication through the serial port

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Module

Newer Serial Communication Technologies:

Universal Serial Bus (USB)

Universal Serial Bus• Being introduced as a high-speed

“replacement” for the traditional RS-232 port

• USB has higher bandwidth– 1.5 Mbps, 12 Mbps and 480 Mbps – Faster than the RS-232 port that

operates in the region of 115+ K bps

• Devices can be daisy-chained

Daisy Chaining of USB Devices

Computer

Device 1

Device 2

Device 3USB Connection

Out

In

USBPort

Connecting USB Devices Using a Hub

Computer

Hub

Device 2

Device 3USB Connection

Out

In

USBPort

Sample USB Devices

• Keyboards• Monitors• Digital Cameras• Digital Vide Recorders• etc.

USB Standards

• USB 1.1• USB 2.0• USB On-The-Go (OTG)

– A newer standard being designed for portable and small devices

U3 Standard

USB Connectors

• Type A– Upstream connectors – From the system

• Type B– Downstream connectors– To the device

• Mini A• Mini B

– Smaller connector for PDAs, mobile phones and digital cameras

• mini-A and mini-B and mini-AB– Small for factor connectors for USB OTG

Support for the Deployment of USB in

Microcomputers• There are two requirements for USB

implementation• One is the presence of USB hubs to

support USB ports on the microcomputer• The other is the support required from

the operating system to operate the USB• Most motherboards now have built-in

support for USB • Not all versions of the Windows OS

support for USB

Operating System Support for USB

• The newer operating systems such as Windows XP or the later versions of some of the older operating systems support USB– Windows 98 – Windows 95 OSR2

• In accordance with USB standards, these operating systems support hot plug-and-play for USB devices

Hot Plug-and-Play

• The ability to connect a device to the computer while a computer is in operation

• As the device is connected, the OS would: – Recognize the device – Configure the device

• There is no manual intervention in the above process

Advantages of USB Over the RS-232 Port

• Higher speed• Ability to daisy chain different

devices• Support for hot plug-and-play

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Module

IEEE 1394 FireWire Connection

IEEE 1394 Standard (FireWire)

• In some ways, it competes with USB• Bandwidth is 400M bps or 50M Bps • In theory therefore, it can replace older

SCSI and IDE used for connecting hard disks

• FireWire’s impact is most likely to be felt in multimedia applications involving audio and video

• Some basic networking can be done through the Firewire ports as well

Data Transmission

• 100 Mbps, 200 Mbps and 400 Mbps • Newer ports are being developed

to support 800 Mbps and 1600 Mbps

• Data is transmitted in packets and it is available to all the devices on the bus

Networking with Firewire

• 1394 supports peer-to-peer networks based on point-to-point connections

• Computers can be networked in a peer-to-peer architecture using the Firewire port

Type of Transmission

• Asynchronous (bulk) transfer - guarantees correct transmission; suitable for control data and where error-free transmission takes precedence over speed.

• Isochronous transfer - guarantees bandwidth (ideal for transmitting time critical data, e.g. video, audio)

• Courtesy: www.thesycon.de

• The maximum distance between nodes is 4.5 m (revisions to the standard will support distances of

• 100 m between nodes• Up to 27 devices can be connected

to each node.• Courtesy: www.thesycon.de

• “Hot-swapping“ allows users to attach and detach devices while the network is running; the network is reconfigured automatically.

• Each bus supports up to 64 nodes and the specification supports up to 1024 buses.

• A 1394 bus appears as a flat space in memory, with each node occupying a 48 bit address range.

• Integrated power supply - devices receive power through the bus.

• Courtesy: www.thesycon.de

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Module

Fiber Channel

End of ModuleEnd of Module

Module

Serial Communication Connections

Unix Computer Connection

ASCIITerminal

Micro-computer

ASCIITerminal

RS-232CConnection

Multi-user Micro (Unix)Multiple serial ports

Multiple Port Support

Interface Card

Multiple Ports

Popular Unix Configuration

Microcomputers as terminals

TCP/IP

Central Unix server

Remote Access Server

Server with Multi-serial Ports

Modem Modem

RS-232CConnection

Modem

Dial-in access

LAN

LapLink Connection

DesktopComputer

Laptop/Notebook/Computer

RS-232C Serial Lap-linkConnection

Note: Lap Link serial cable is specially wired to make the connection

X.25 Standard

• Used in WAN connections• X.25 is used in the U.S.• Its equivalent X.21 is used in Europe• Today, the above older technologies

are being replaced with newer digital technologies– ATM – Frame Relay etc.

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Module

Parallel Communication

Definition of Parallel Communication

• Transmission of information over multiple links between two points– Multiple electronic links

Parallel Transmission

Multiplelinks

IEEE 488 Parallel Standard• Established by IEEE• Used extensively in parallel

Communication• Examples:

– Computer to printer connection– Lap Link connection

• Does not play as important a role as the serial standard– Hardly any parallel long distance links in

practice

Parallel Port and Serial Ports in a Microcomputer

DB25F

DB9M

DB25M

Serial Com1:

Serial Com2:

Parallel LPT1:

Parallel Port Resources

• Resources must also be assigned to the parallel port as well– IRQ and I/O address range

• Sample values assigned for LPT1– IRQ 7 – I/O address range 378 - 37f– These values should not be changed

in general

Summary• A microcomputer is equipped with one

standard parallel port• Additional parallel ports can be installed• Used extensively for connecting a printer

– Used for connecting other devices as well

• Needs to be assigned resources• Identified by the DB25 female connector

Parallel Port Resource Assignment

Demonstration

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Module

Newer and Faster Parallel Port Standards

Popular Introductions

• Standard Parallel Port (SPP)• Enhanced Parallel Port (EPP)• Extended Capability Port (ECP)

EPP and ECP

• Enhanced Parallel Port (EPP)– Introduced in 1991 to increase the parallel

port communication speed to 500K Bps

• Extended Capability Port (ECP)– Introduced further refinement to the EPP– For better performance under a

multitasking environment– Introduced through a joint effort between

Microsoft and HP

Support for EPP and ECP • Must be built into the hardware namely

into the motherboard• Activated at the system level by

enabling the support for EPP and ECP in the system BIOS

• For example, the System BIOS can be accessed during boot-up by pressing the delete key immediately after switching on the power to the computer

Other Features Supported

• Wake-up signal sent to the printer• Consider the case of a newer laser

printer that is attached to a microcomputer through an ECP port– Printer must also be connected to the

microcomputer using a cable conforming to the IEEE specification

Wake Up Feature

• No printing activity for a predetermined period of time– Printer enters into a sleep mode– Printer does not consume power

• When a print job is ready for printing– Computer sends a signal to wake up

the printer– The printing then proceeds thereafter

Salient Features of EPP and ECP

• EPP was introduced to increase the speed of the parallel port

• ECP was introduced to add further enhancements to EPP– Improve the performance under

multitasking

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Module

ECP Computer Entry

ECP Entry Check

End of ModuleEnd of Module

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