GATE CSE 1995 | Question: 17a

Question

An asynchronous serial communication controller that uses a start-stop scheme for controlling the serial I/O of a system is programmed for a string of length seven bits, one parity bit (odd parity) and one stop bit. The transmission rate is $1200$ bits/second.

1. What is the complete bit stream that is transmitted for the string $‘0110101’?$

2. How many such string can be transmitted per second?

Answer 1

1. The complete bit stream will be $1011010111$ [First bit is Start bit; Last bit is Stop bit preceded by Parity bit which is $1$ as odd parity is used and data is of $7$ bits]
2. Bandwidth is given as $1200$ bits/sec
   One complete bit stream is of length $10$ bits $(1$ Start bit, $7$ bit String, $1$ Parity bit, $1$ Stop bit)
   So, in $1$ second we can send $\frac{1200}{10}=120$ Strings.

Comments

If we consider this question  https://gateoverflow.in/815/gate2002-1-11

then answer to part $i)$ must change. Isn't ?

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Okay. I think inorder to make odd-parity we might have to consider 1 as start bit too.

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Kushagra गुप्ता in order to consider odd parity when first bit is 0, can't parity bit be made 0 ?

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I think start bit here is chosen as 1 because given bit stream starts with 0. If start bit is 0 then receiver may mistake it as start of the bit stream.