CHAPTER Serial and Parallel Communication

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 series AB 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 Digital Data Serial Digital Data Out In Expansion Bus Serial Interface

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 Female Port

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 PORTIRQADDRESS F8-3FF 232F8-2FF 3 4 These values should not normally be changed.

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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 UART 16550/ 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 3 USB Connection Out In USB Port

Connecting USB Devices Using a Hub Computer Hub Device 2 Device 3 USB Connection Out In USB Port

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:

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:

“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:

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Module Fiber Channel

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Module Serial Communication Connections

Unix Computer Connection ASCII Terminal Micro- computer ASCII Terminal RS-232C Connection 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 RS-232C Connection Modem Dial-in access LAN

LapLink Connection Desktop Computer Laptop/ Notebook/ Computer RS-232C Serial Lap-link Connection 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 Multiple links

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 f –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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