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s used for all long-haul communication and most computer networks, where the cost of cable and synchronization difficulties makes parallel communication impractical. Serial computer buses are becoming more common as improved technology enables them to transfer data at higher speeds.

4.3.1Synchronization

In order to transmit data between two devices it must be necessary that the data must be synchronized. Synchronization needs to be done so that the receiving system have an idea from where the first byte starts and where it ends,

4.3.1.1 Methods of Synchronization

There are two ways to synchronize the two ends of the communication.

Synchronous transmission
Asynchronous transmission
4.3.1.1.1 Synchronous Transmission

In synchronous transmission a continuous stream of data is sent at regular intervals. A clock is used which synchronize the receiver with the transmitter. The data is transferred in the form of packets. Each packet contains

Start frame
Stop frame
Data
The function of start frame is to indicate the arrival of a new packet and secondly synchronized with the receiver clock. The function of end frame is to indicate that the end bits of the message when the data ends. Data is present between the start frame and the stop frame. The maximum bits of data in a packet are 64,000 bits.

End Frame

Data (Max 8K bytes)

Start Frame

There are two methods of synchronous transmission.

Data/strobe synchronous transmission
In this type of transmission stream of data is put on one wire and pulse of voltage on other wire (strobe). This tells the receiver about the start and stop bits.

Single wire synchronous transmission

In this type of transmission a single wire is used to transmit the signal. Manchester code is the example of this transmission. One is indicated when signal shifted from a low state to a high state and zero is indicated on switching from high to low state.

The major advantage of synchronous transmission is that fewer overheads are required to send data with greater efficiency and less chance of loss of synchronization. But at the same time it is more difficult to implement and is also costly.

4.3.1.1.2 Asynchronous Transmission

In asynchronous transmission, signal is transmitted on a signal wire. The periodic stream of data is transmitted by the transmitter and is distinguished by the receiver as a sync signal.

In asynchronous transmission seven or eight bit of data are transmitted in the form of ASCII characters. The character specifies the start and stop bits. E.g. “1000 0101” is transmitted as “1 1000 0101 0” with 1 as start bit and 0 as stop bit. A parity bit can also be included in the data stream.

0

8

7

6

5

4

3

2

1

1

Stop bit

Start bit

4.4Universal Asynchronous Receiver/Transmitter

A Universal Asynchronous receiver/transmitter (UART) is a type of asynchronous transmitter receiver. It translates the data in serial and parallel form and is commonly used in microcontrollers.

For serial communication fo