Interfaces - mskarande.files.wordpress.com › 2015 › 01 › chap... · Subject : Computer...

Subject : Computer Hardware and Maintenance (17428)

Compiled By : Ms. M.S.Karande (I/c HOD-IF) of 21

6

Interfaces



1) SCSI

SCSI(Small Computer System interface) is a set of standards for physically connecting and transferring data between computers and peripheral devices.

SCSI is most commonly used for hard disks and tape drives, but it can connect a wide range of other devices, including scanners and optical drives(CD, DVD etc.)



SCSI is basically a bus into which different peripherals are connected in daisy chain

SCSI Connector

SCSI is not device level interface it is system level interface

System level interfacing is not based on any specific device instead it uses signals that are converted from device level signals to the signals used by the host computer system. Hence it can require HDD, printer, scanner etc.

Upto 8 subsystems can exist on a SCSI bus

It is used in special servers and RISC systems

http://computer.howstuffworks.com/enlarge-image.htm?terms=scsi&page=0



SCSI Controller

There are 3 different SCSI standards SCSI-1, SCSI-2, SCSI-3

SCSI-1:

1. The original specification developed in 1986, SCSI-1 is now obsolete.

2. It featured a bus width of 8 bits and clock speed of 5 MHz.

3. 8 bit parallel bus

4. 50 pin cable

SCSI-2:

1. Adopted in 1994, this specification included the Common Command Set (CCS) -- 18 commands considered an absolute necessity for support of any SCSI device.

2. It also had the option to double the clock speed to 10 MHz (Fast), double the bus width from to 16 bits and increase the number of devices to 15 (Wide), or do both (Fast/Wide).

3. SCSI-2 also added command queuing, allowing devices to store and prioritize commands from the host computer.

4. High density 50 pin cable connectors.



SCSI-3:

1. This specification debuted in 1995 and included a series of smaller standards within its overall scope.

2. A set of standards involving the SCSI Parallel Interface (SPI), which is the way that SCSI devices communicate with each other, has continued to evolve within SCSI-3.

3. Most SCSI-3 specifications begin with the term Ultra, such as Ultra for SPI variations, Ultra2 for SPI-2 variations and Ultra3 for SPI-3 variations.

4. The Fast and Wide designations work just like their SCSI-2 counterparts. SCSI-3 is the standard currently in use.

Name Specification # of

Devices Bus

Width Bus

Speed MBps

Asynchronous SCSI

SCSI-1 8 8 bits 5 MHz 4 MBps

Synchronous SCSI

SCSI-1 8 8 bits 5 MHz 5 MBps

Wide SCSI-2 16 16 bits

5 MHz 10 MBps

Fast SCSI-2 8 8 bits 10

MHz 10 MBps

Fast/Wide SCSI-2 16 16 bits

10 MHz

20 MBps

Ultra SCSI-3

SPI 8 8 bits

20 MHz

20 MBps

Ultra/Wide SCSI-3

SPI 8

16 bits

20 MHz

40 MBps

Ultra2 SCSI-3 SPI-2

8 8 bits 40

MHz 40 MBps

Ultra2/Wide SCSI-3 SPI-2

16 16 bits

40 MHz

80 MBps

Ultra3 SCSI-3 SPI-3

16 16 bits

40 MHz

160 MBps

Ultra320 SCSI-3 SPI-4

16 16 bits

80 MHz

320 MBps



SCSI Cables

i. It includes the wire, connectors and possibly a terminator as well.

ii. SCSI cable come into distinct varieties : external and internal

a. External

b. Internal

External Cables:

i) External cables are used to connect SCSI devices that do not reside inside the PC, but rather have their own enclosures an power supplies.

ii) These are generally expensive.

Internal Cables

Internal cables connect SCSI devices installed within the PC system box.

Internal SCSI devices connect to a ribbon cable

External SCSI devices connect using thick, round cables



External Connector types:

a. D-Shell(D-Sub, DD)

i. The earliest SCSI standard SCSI-1 defined a 50-pin D-shell connector for narrow SCSI implementations

ii. The name of this connector comes from the D-shaped metal shell that goes around the pins on the male half of the connector

iii. This is obsolete because it was large and cumbersome .

DD-50 SCSI Connector

b. Centronics (Alternative 2)

The other external connector type defines by the SCSI-1 standard is 50-pin connector that is commonly called a Centronics connector, after a formerly popular printer that used this type of connector.

Two latches on either side are used to hold the connector in place.

These 50-pin connectors are still present in the current SCSI specification and are called Alternative 2 external connectors.

50-pin Centronics SCSI connector



c. High Density (HD) [ SCSI-2 50 pin version (Alternative 1)

68-pin (Alternative 3)]

These are high-density shielded connectors in SCSI-2 These are really not all that different from the older D-shell connectors but the space between pins was reduced making the connectors smaller cheaper to make and easier to use

68-pin Alternative 3 SCSI connector

d) Very High Density Cable Interconnect (VHDCI) [Alternative 4]

This connector is wide only (68 pins) and is sometimes called a”micro-Centronics connectors , because it uses the same design as the Centronics connectors only with the contacts much smaller and closer together.

These are Alternative 4 for external connectors and is growing in popularity because of its small size.

A male 68-pin VHDCI connector.



SCSI Drive Configuration

The following items need to be set up for configuring a SCSI Drive. They are, 1. Set SCSI Device ID 2. Activate the termination jumper to the device which is present at

the end of the chain. 3. Disable auto start 4. Delay auto start 5. Stagger spin: it is an enhanced version of Delay Auto Start. It

should be configured if many hard disk are attached to the system 6. Narrow/Wide mode 7. Force SE : Allow newer Ultra 2,Wide Ultra 2,Ultra 160, Ultra 160+

or other LVD(low voltage differential) SCSI drives to be forced to use single-ended (SE) operation. SCSI Bus Signaling: Three types of Signaling SE or Single Ended: Card sends a single pulse, each device taking part of the signal. Degrades rapidly. (10 ft) HVD or High Voltage Differential; Two data lines, each device re-transmits signal down line. (up to about 80 feet) LVD or Low Voltage Differential; Same principle as HVD but smaller re-transmitters, lower voltage. More cost effective, but shorter length of chain (40 feet)

8. Disable parity.



USB

Just about any computer that you buy today comes with one or more

A sample list of USB devices that you can buy today includes:

Printers

Scanners

Mice

Joysticks

Flight yokes

Digital cameras

Webcams

Scientific data acquisition devices

Modems

Speakers

Telephones

Video phones

Storage devices such as Zip drives



Network connections

Data Rates

Low Speed: 1.5 Mbps (Keyboards, mice, etc.)

Full Speed: 12 Mbps (USB1.1 max speed)

Hi-Speed: 480 Mbps (USB2.0 max speed)

Super Speed : 4.8 Gbits/s (600 MB/s) (USB 3.0 max rate)

A typical USB connector, called an "A" connection

Many USB devices come with their own built-in cable, and the cable has an "A" connection on it. If not, then the device has a socket on it that accepts a USB "B" connector.

A typical "B" connection

The USB standard uses "A" and "B" connectors to avoid confusion:

"A" connectors head "upstream" toward the computer.

"B" connectors head "downstream" and connect to individual devices.



USB Features

The Universal Serial Bus has the following features:

The computer acts as the host.

Up to 127 devices can connect to the host, either directly or by way of USB hubs.

Individual USB cables can run as long as 5 meters; with hubs, devices can be up to 30 meters (six cables' worth) away from the host.

With USB 2, the bus has a maximum data rate of 480 megabits per second.

A USB cable has two wires for power (+5 volts and ground) and a twisted pair of wires to carry the data.

On the power wires, the computer can supply up to 500 milliamps of power at 5 volts.

Low-power devices (such as mice) can draw their power directly from the bus. High-power devices (such as printers) have their own power supplies and draw minimal power from the bus. Hubs can have their own power supplies to provide power to devices connected to the hub.

USB devices are hot-swappable, meaning you can plug them into the bus and unplug them any time.

Many USB devices can be put to sleep by the host computer when the computer enters a power-saving mode.

The devices connected to a USB port rely on the USB cable to carry power and data.



RS232 (RS- Recommended Standard)

Is a standard interface developed by Electronics Industries Association

Uses asynchronous serial Communication

It is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment eg: Computer) and a DCE (Data Communication Equipment eg: modem). It is commonly used in computer serial ports.

RS 232 Voltage Level:

Follows Negative Logic

Logic 1 represents a negative voltage

Logic 0 represents a positive voltage

Logic 1 (-3V to -15V)

Logic 0 (+3 V to +15V)

RS 232 Signals

Sr No

Pin No

Signal Signal Name Source Destination

1 1 ----- Frame Ground

--- ----

2 2 TXD Transmit Data DTE DCE

3 3 RXD Receive Data DCE DTE

4 4 RTS Request to Send

DTE DCE

5 5 CTS Clear to Send DCE DTE

6 6 DSR Data Set Ready

DCE DTE

7 7 SG Signal Ground --- ----

8 8 RLSD or CD

Received Line Signal Detect

DCE DTE

9 20 DTR Data Terminal Ready

DTE DCE

10 22 RI Ring Indicator DCE DTE



CD (Carrier Detect or Data Carrier Detect) : It is used by computer to know that the modem connected to the serial port has made proper connection with modem on the other side.

RxD(Receive Data) : It is used by the device connected to the serial port to send data to the computer Or data send from DCE to DTE

TxD(Transmit Data): It is used by the computer to send data to a device connected to the serial port Or Data sent from DTE to DCE

DTR(Data Terminal Ready): It is send from computer to the device connected to the serial port to inform that computer is ready for communication

GND(Signal Ground) This is one of the most important signal. This wire provides the necessary return path for both the data signals and the hand shaking signals.



DSR(Data Set Ready): It is send from the device connected to the serial port to the computer to inform that the device is ready for communication

RTS(Request To Send):One clear to send signal is received the computer send Request To Send(RTS) signal to the device connected to the serial port to inform that computer is also ready to start the data transmission

CTS(Clear To send): Clear to send or CTS signal is used by the device connected to the serial port to inform to the computer can start the data transmission.

RI(Ring Indicator): RI Signal is used by the device connected to the serial port to inform to the computer that it has detected a ringing voltage on the telephone line. This signal is used by a modem connected to the serial port to inform to the computer that someone is calling the modem.



Centronics interface

The Centronics parallel interface is an older and still widely-used standard I/O interface for connecting printer s and certain other devices to computers.

Signals in Centronics interface

Data Lines

Busy

PE (No Paper)

SLCT (Selected)

Print Controller

(Computer

Side)

Printer

Side

INIT (RESET)

AUTO FEED XT(Hardware line feed

SLCT IN (Enable interface)

ERROR (Fault)

ACK Give Data)

Ground

STROBE (take Data)



Signals from PC to Printer

There are 12 signals from the PC to the printer. Out of these 8 signals are data bits and 4 signals are control signals. These are

1) STROBE The printer should take data when this signal is low.

2) INIT When it is low the printer resets its electronics logic and clear the printer buffer

3) SLCTIN It is an interface enable signal when this signal is low the printer responds to signals from the controller

4) AUTO FEED XT After printing every line the printer will provide one line feed automatically if this signal is low. This type of line feed known as hardware line feed.

Signals from printer to PC

There are 5 status signals from the printer to the PC. These are

ACK

This Signal is an acknowledgement for STROBE Signal from PC. When active, it indicates that printer has received data sent by the PC and the printer is ready to accept next data byte

BUSY

When BUSY Signal is high it indicates that the printer is busy and it cannot receive data. This signal becomes high under any of the four signals

1) On Receiving STROBE active 2) During printing operation 3) When the printer is in offline start 4) When the printer senses some error condition

PE When PE Signal is high it indicates that there is no paper in the printer

SLCT SLCT Signal indicates that the printer is selected and logically connected to PC

ERROR

ERROR signal indicates that there is some error condition in the printer. This signal becomes active under any of the following three reasons:

1) Mechanical fault or electronic fault in the printer

2) The printer is in offline state

3) There is no paper in the printer



Firewire (IEEE 1394)

Firewire, also known as IEEE 1394 and i.Link, is a high speed serial bus developed by Texas Instruments and Apple computers in the mid 1990s.

Firewire is compatible with more than 63 electronic and digital devices, which makes it a great choice for many people.

Technically speaking, Firewire is a PC serial bus interface standard that offers isochronous data services (guarantees timely delivery of data between the nodes) and high-speed communications between digital devices.

Basically, Firewire facilitates faster data transfer rates and usability across multiple devices.

Firewire is similar to Universal Serial Bus (USB), but it has a higher data transfer capacity - up to 800 Mbps, compared to the USB's 480 Mbps.

This makes it ideal for peripherals that require high-speed data transfer, such as digital camcorders, DVD players and digital audio equipment.

Firewire 400, the first model to be introduced, had data transfer speeds of 100, 200, and 400 Mbps.

Firewire 800 was introduced in 2003 and has a transfer rate of 800 Mbps, it also comes with a six pin connector that makes it compatible with the earlier Firewire 400.

Thanks to the low start up costs and more adaptable cabling system, Firewire has successfully replaced SCSI in many applications.

Firewire is widely used in situations where there is simply a need for data transfer at the highest speeds possible. Most personal computers come in with a built in Firewire port, as do many MP3 players.

Firewire gets a lot of positive recognition because it provides high speed, better power distribution, and does not require a computer host for its functioning.

Firewire also gets a lot of attention because it outdoes SCSI capabilities in the way of higher sustained data transfer rates, which audio and video editors require. Most would also agree that the Firewire is advantageous because it can be daisy chained to extend it to many times a single cable length.

Compared to SCSI or USB, it can be seen that Firewire easily outperforms the other technologies because it is more robust, efficient, and has some great features. Some of the great things are that Firewire can be used to connect 63 peripherals in a cyclic network structure where SCSI follows a linear structure.

Firewire also facilitates peer-to-peer device communications without



using PC memory.

Firewire also permits multiple hosts per bus, without the aid of an additional chip set like a USB cable. Firewire also supports plug and play and acts as a useful power cord for moderately power consuming devices.

Used with Digital Camera, DV Camcorders, HDTV, High-Speed Drives, DVD players and digital audio equipment

Bluetooth

Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers (desktop and laptop), cameras, printers, coffeemakers. A Bluetooth LAN is an adhoc network, which means that the

Network is formed spontaneously; the devices, sometimes called gadgets, find each other and make a network called a piconet.

Bluetooth technology has several applications. Peripheral devices such as a wireless mouse or keyboard can communicate with the computer through this technology.



Monitoring devices can communicate with sensor devices in a small health care center.

Home security devices can use this technology to connect different sensors to the main

Security controller. Conference attendees can synchronize their laptop computers at a conference.

Bluetooth was originally started as a project by the Ericsson Company.

It is named for Harald Blaatand, the king of Denmark (940-981) who united Denmark and Norway.

Blaatand translates to Bluetooth in English.

Today, Bluetooth technology is the implementation of a protocol defined by the IEEE 802.15 standard. The standard defines a wireless personal-area network (PAN).

Operable in an area the size of a room or a hall

Bluetooth defines two types of networks: piconet and scatternet.

Piconets

A Bluetooth network is called a piconet , or a small net. A piconet can have upto eight stations, one of which is called the primary; the rest are called secondaries. All the secondary



stations synchronize their clocks and hopping sequence with the primary.

Note that a piconet can have only one primary station. The communication between the

Primary and the secondary can be one-to-one or one-to-many.

Scatternet

Piconets can be combined to form what is called a scatternet. A secondary station in one piconet can be the primary in another piconet.

This station can receive messages from the primary in the first piconet(as a secondary) and, acting as a primary, deliver them to secondaries in the second piconet.

A station can be a member of two piconets.

The literature sometimes uses the terms master and slave instead of primary and secondary.

Interfaces - mskarande.files.wordpress.com › 2015 › 01 › chap... · Subject : Computer...

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