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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