MAYURBHANJ SCHOOL OF ENGINEEING

PREPEARED BY:- BIBHUDENDRA SARANGI

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TOPIC-CONNECTION AND INTERFACING

3.CONNECTION AND INTERFACING

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Based on the number of bits transmitted at a time Data transmission is divided into 2 types

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1. Serial Transmission
2. Parallel Transmission

Serial Transmission

• When data is transmitted serially i.e. one bit at a time is called Serial Transmission. Only one wire is used for the data transmission in any particular transmission. Data bits are transmitted one after another. If we want to transmit one byte of data from transmitter to receiver, each bit will be transmitted one after another and hence will take 8 time units.

Transmitter

Receiver

Tx

Rx

Tx

Rx

GND

GND

Transmission Link in Serial Transmission

Parallel Transmission

• In parallel transmission several bits are transmitted simultaneously over the multiple transmission lines. The number of bits which are transmitted simultaneously depends on the design of the system. If we are dealing with a computer dealing with ASCII code we need to design the transmission link with 8 separate wires (7 bits + 1 parity bit). Each wire will carry one bit at a time. Additional wire is required for control signals.

Transmission link for Parellel Transmission

Transmitter

Receiver

D 1

D 2

D 3

D 4

D 5

D 6

D 7

D 8

Clock / Strobe

If we compare these two systems we can easily observe the followings

• Serial mode is less costly as it requires only one wire for data as compared to many wires in parallel mode.

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• Parallel transmission speed is much higher than serial transmission as it transmits ‘n’ bits at a time compared to 1 bit in serial mode.

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• Parallel transmission throughput is higher in compare to serial transmission.

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Due to cost and other factors serial transmission is used for long distance communication system whereas parallel transmission is restricted to short distance communication

Data Transmission modes

There are three ways or modes for transmitting data from one point to another. They are –

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• Simplex

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• Half – Duplex

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• Full - Duplex

Simplex Mode

• In this mode data is transmitted in one direction only. This means that one end will always be a transmitter while the other end will always be a receiver. Both the transmitter and the receiver never change their status.

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Tx

Rx

One direction at all the time

Half – Duplex Mode

• In this mode data is allow to flow from both the ends. But not simultaneously. When the transmitter transmits data, it can not receive data, similarly when the receiver receiving data it can not send data. When the receiver ends receiving data, it will change its status to a transmitter and can send data to the other end. Similarly the transmitter will change its status and receive data as a receiver. The changing of status from receiver to transmitter or transmitter to receiver is known as “Turn Around” and the time taken for this is known as Turn Around time.

Tx

Rx

One direction at a time

Full Duplex mode

A transmission system in which data can be transmitted in both directions simultaneously is called a full duplex system. It is also called Duplex mode. Full duplex mode provides maximum function and performance to a transmission link

Tx

Rx

Both direction at the same time

Parallel Connection

The serial transmission approach is perhaps the most frequently used technique. However it does have the disadvantage that each byte of information take eight time slots to be transmitted. Over relatively shorter distance like a PC and its printer it is possible to have eight separate wires and so we could send each bit of a byte simultaneously. Each wire carries one bit of the character. This approach is known as parallel transmission

Character (n +3)

Character (n +2)

Character (n +1)

Character (n )

Parallel transmission

• As each individual wire has slightly different properties there is a possibility that data could travel at marginally different speeds over each of the wires. This introduces the problem of SKEW where the signal for each bit of the character arrives at the destination at a marginally different time from the other.

Skew

• Ideally we need to clock all eight transmission lines at the receiving end simultaneously, so we can not allow any significant skew to develop. Hence we tend to keep the length of parallel transmission fairly short. Higher costs are also associated with the cabling and interfacing of the parallel approach. Consequently parallel transmission is normally only used over short distance between two devices where the advantage of speed over the serial transmission technique may be desirable.