View Full Version : uart

07-02-2005, 02:27 PM
how is asynchronous data synchronised
i read somewhere that some extra bits a r added for synchronising
couldn't understand how that helps
and wht is the need of synchronising at all
pls also explain diferences between the 2

07-02-2005, 11:06 PM
Asynchronous uses start/stop bits to mark a packet(byte)..whereas synchronous uses a string of characters to stay in sync.

Consider this setup:
A microcontroller and a PC communicating with each other..
There is a term known as "BAUD rate"..u set both the PC and the micro to a baud rate ,say, at 9600bps
Now since both run at the same baud rate(on their respective side)..there isnt a synchronisation signal needed
hence Asynchronous..

i read somewhere that some extra bits a r added for synchronising

whenever your transmitting data,ur supposed to first send a start bit followed by your 8 bit data and then your stop bit
This forms a packet(a total of 10 bits)

At the receiver side(here for eg the PC)..waits for a START bit..then counts the 8 bits of data comin in.The STOP bit signals the end of the packet.

07-04-2005, 04:55 PM
but then wht is the need of synchronising
it would be better if u cld explain exactly wht is meant of synchronising and how it helps or tell some link where thwese cbts can be clrd

07-04-2005, 05:27 PM
but then wht is the need of synchronising
If you dont synchronise data when 2 devices communicate with each other,
you will never get the data across

Maybe these pages will help


07-06-2005, 09:53 AM
well i read the links were quite helping but the basic problem with me is wht exactly is meant by synchronisation of data here.i might be irritating for u but i need to know this

12-09-2005, 01:37 AM
Hey synchronization means two devices being tuned up to send and receive the data.

For example take a case wheren we do not synchronize the process, then a case might occur where the sender sends the data earlier to the receiver . In this case the receiver might miss a few bits.

So by synchronization we mean (in a very raw way ) that both devices starting the process at same time.

12-09-2005, 10:18 AM
If you are an engineering student..

then synchronization means.. both devices share the same clock..

If you are just a lay man then. synchronization means..
both devices are dancers and they are dancing the same steps on the same beats..


06-02-2006, 01:34 AM
Wow Rao! You should be a lecturer dude :wink:

06-02-2006, 10:56 AM
asynchronous communication means there is no clock.

In synchronous communication b/w two devices there is a clock pin and mostly one act as the master and other as slave and master produces the clock.

In asynchronous communication speed of both of them are same. Now ur questions is tht how it happens. Let's take the example of UART of computer or microcontroller. The receiver of one is tied with transmit of other. If there is no communication voltage on the line is high. If you want to transmit some data, there is a data format first bit LOW 8 bit data then one stop bit. Suppose if the transmitter want to send data. It first make the line LOW for 1/baud time. This makes the receiver to sense that some data is on the line and receiver understands tht the next data are the 8 data bits and one stop bit and receiver receives the data and stop bits in an interval time of 1/baud. It check whether the format is same. i.e, is it LOW 8data bits and 1 stop bit. If it is false then receiver interpret tht the data is wrong.

But in this case the speed and protocols of both transmitter and receiver should be same. Read serial port communication, then u will understand better

Bibin John