GATE CSE 2002 | Question: 1.11

Question

In serial data transmission, every byte of data is padded with a $'0'$ in the beginning and one or two $'1'$s at the end of byte because:

• A. receiver is to be synchronized for byte reception
• B. receiver recovers lost $'0'$s and $'1'$s from these padded bits
• C. padded bits are useful in parity computation
• D. none of the above

Comments

NEVER HEARD OF THIS CONCEPT
IS THIS STILL IN SYLLABUS

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@Sherlock_Holmes

Yes Holmes, it is out of syllabus 

Answer 1

Answer (A) In serial communication in beginning $'0'$ is padded as start bit and one or two $'1'$s are padded as stop bit.

and those bits are for synchronize receiver

http://esd.cs.ucr.edu/labs/serial/serial.html

Comments

the stop bits can be 1 or 2

Answer 2

This question is describing the classic asynchronous serial communication frame. Because the sender and receiver do not share a separate "clock" wire to keep their timing perfectly matched, they are completely out of sync.

The padded bits act as the timing mechanism to fix this:

• The padded '0' at the beginning is the Start Bit: The line idles at a high voltage ('1'). When the sender forces it to a low voltage ('0'), it acts as a wake-up call. The exact moment the receiver feels that voltage drop, it synchronizes its internal clock and starts a timer to read the incoming 8 bits of data at the agreed-upon baud rate.

• The padded '1's at the end are the Stop Bits: By forcing the line back to a high voltage ('1'), it officially ends the frame. This gives the receiver time to process the byte, and crucially, it guarantees the line is back at an idle '1' state so the next Start Bit ('0') can be easily detected.

Why the other options are wrong:

• Recovering lost bits: Start and stop bits cannot magically recover a corrupted data payload. If a bit flips in the middle of transmission, it is lost or corrupted.

• Parity computation: Parity is an entirely separate, optional bit inserted before the stop bits. The start and stop bits are never used to calculate parity.

Answer 3

answer must be (D)

-bcoz reciever is to be synchronized for bit reception not for byte reception