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
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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
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