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CHAPTER 2

DEVICES AND COMMUNICATION

BUSES FOR DEVICES NETWORK

I/O PORT TYPES

Types of Serial ports

Synchronous Serial Input

Synchronous Serial Output

Asynchronous Serial UART input

Asynchronous Serial UART output

TYPES OF PARALLEL PORTS

Parallel port one bit Input

Parallel one bit output

Parallel Port multi-bit Input

Parallel Port multi-bit Output

SYNCHRONOUS SERIAL INPUT

SYNCHRONOUS SERIAL OUTPUT

SYNCHRONOUS SERIAL INPUT/OUTPUT

ASYNCHRONOUS SERIAL INPUT

ASYNCHRONOUS SERIAL OUTPUT

TWO MODES OF COMMUNICATION BETWEEN

DEVICES AND COMPUTER SYSTEM

Full Duplex – Both devices or device and

computer system simultaneously communicate

each other

Half Duplex – Only one device can

communicate with another at an instance

TEN WAYS OF TRANSMITTING SYNCHRONOUS

SERIAL BITS

ASYNCHRONOUS COMMUNICATION

Clocks of the receiver and transmitter

independent, unsynchronized

Ex: UART Serial, Telephone or modem

Communication, RS232C communication

between the UART devices.

RS232C COMMUNICATION

RS232C COMMUNICATION

When a modem connects, modem sends data

carrier detect DCD signal at an instance t0.

Communicates data set ready (DSR) signal at

an instance t1 when it receives the bytes on

the line.

Receiving computer (terminal) responds at an

instance t2 by data terminal ready (DTR) signal.

After DTR, request to send (RTS) signal is sent

at an instance t3

RS232C COMMUNICATION

Receiving end responds by clear to send (CTS)

signal at an instance t4. After the response

CTS, the data bits are transmitted by modem

from an instance t5 to the receiver terminal.

PROTOCOL

A protocol is a standard adopted, which tells the way in which the bits of a frame must be sent from a device (or controller or port or processor) to another

HDLC, Frame Relay, for synchronous communication device or system.

For asynchronous transmission from a device port− RS232C, UART, X.25, ATM, DSL and ADSL

Ethernet and token ring protocols used in LAN networks

HDLC(HIGH LEVEL DATA LINK CONTROL)

It is bit oriented protocol

Support both half and full duplex mode in point to point and multipoint

HDLC are characterized by

Station type

Primary station, secondary and combined station

Configuration

Unbalanced , symmetrical and balance configuration

HDLC(CONTINUED)

Normal response mode, asynchronous

balanced mode

Frame type

I –frame

S- frame

U- frame

HDLC(CONTINUED)

Flag field : 8 bit sequence with bit pattern 01111110 that identifies both the beginning and end of the frame and serves as synchronization pattern for the receiver

Address field: it contains the address of the secondary station.

Control field: it its 1 or 2 byte segment of the frame for flow and error control.

Information field: data from network layer

FCS field: error detecting field

HDLC(CONTINUED)

HDLC(CONTINUED)

The first field defines the type

N(s) represents sequence number of the frame

N(r) represents acknowledgement number

when piggybacking is used

P/F it means poll if frame is sent from P to S

And final if frame is sent from S to P

Code in S frame : RR(receiver ready 00),

RNR(receiver not ready 10), REJ(reject 01),

SREJ(selective reject 11)

HDLC(CONTINUED)

I frames are used to transfer user data and

control information relating to user data

S frames are used to transfer control

information

U frames are reserved for system management

and managing the link itself

SPI( SYNCHRONOUS PERIPHERAL INTERFACE)

Full-duplex Synchronous communication.

SCLK, MOSI and MISO

Device selection as master or slave can be

done by a signal to hardware input SS.

(Slave select when 0) pin

SPI( SYNCHRONOUS PERIPHERAL INTERFACE)

SCI(SERIAL CONNECT INTERFACE)

UART asynchronous mode port Full-duplex

mode

SCI programmable for transmission and for

reception

SI(SERIAL INTERFACE)

SI is synchronous- asynchronous serial

communication port called USART

SDIO(SECURE DIGITAL INPUT OUTPUT)

PARALLEL PORT AT DEVICES

8-bit IOs

Short distances, generally within a circuit board or IC or nearby external devices

Advantage− Number of 8 bits over the wires in parallel.

High data transfer rate

Disadvantage− More number of wires

High capacitance results in delay

High capacitance can also result in noise and cross talk

PORT INTERFACING

PARALLEL IO PORT HANDSHAKING AND

INTERFACING

INTEL 8255 PROGRAMMABLE PERIPHERAL

INTERFACE(PPI)

Intel 8255 provides 24 parallel input/output pins.

Used in many microcomputer/microcontroller system

24 pins are divided into three 8-bit ports

Port A and Port B can be used as an 8 bit i/o port

Port c can be used as two 4 bit i/o ports or produce handshake signals for port A and B or 8 bit i/o port

INTEL 8255 PROGRAMMABLE PERIPHERAL

INTERFACE(PPI)

Alternatively, the ports can be grouped as

Group A (Port A and Port C upper four bits)

Group B (Port B and Port C lower four bits).

Eight data lines are available to read/write data

into ports or CR under the status of RD’ and

WR’ Pins.

Address lines A0 and A1 allow access a data

register for each port or CR.

00-Port A, 01- Port B, 10- Port C, 11-CR.

INTEL 8255 PROGRAMMABLE PERIPHERAL

INTERFACE(PPI)

8255 has three different operating modes −

Mode 0 − In this mode, Port A and B is used as

two 8-bit ports and Port C as two 4-bit ports.

Mode 1 − In this mode, Port A and B is used as

8-bit I/O ports. They can be configured as

either input or output ports.

Mode 2 − In this mode, Port A can be

configured as the bidirectional port and Port B

either in Mode 0 or Mode 1.

SOPHISTICATED INTERFACING

FEATURES IN DEVICE PORTS

In built schmitt trigger circuit is used to

conditioning the signal to noise elimination.

Datagate(xililnx) to reduce power dissipation

when device are operated at high speeds.

Device for I/O may integrate a SerDes

(serialization and De-serialization) subunit.

HTTP

hypertext transfer protocol

It is an application layer protocol that allows

web based applications to communicate and

exchange data.

It is TCP/IP based protocol

Features : connectionless, stateless, any data

Working of HTTP

HTTP

HTTP contains three main section: start line,

headers, body which contains plain text

information and binary data

Information is depended on the http message

whether it is a request or response.

TCP/IP PROTOCOL

Transmission control protocol and internet

protocol

UDP PROTOCOL

UDP PROTOCOL

TCP/IP PROTOCOL

TCP/IP PROTOCOL