When the transmitter wishes to send data, it first places the line

in a space level (i.e. the complement of a mark) for one element period. This element is called the start bit and has a duration of T seconds. The transmitter then sends the character, l bit at a time, by placing each successive bit on the line for a duration of T seconds, until all bits have been transmitted. Then a single parity bit is calculated by the transmitter and sent after the data bits. Finally, the transmitter sends a stop bit at a mark level (i.e. the same level as the idle state) for one or two bit periods. Now the transmitter may send another character whenever it wishes.

At the receiving end of an asynchronous serial data link, the receiver continually monitors the line looking for a start bit. Once the start bit has been detected, the receiver waits until the end of the start bit and then samples the next N bits at their centers, using a clock generated locally by the receiver. As each incoming bit is sampled, it is used to construct a new character. When the received character has been assembled, its parity is calculated and compared with the received parity bit following the character. If they are not equal, a parity error flag is set to indicate a transmission error.

(1).When the transmitter wishes to send data, it first sends().

A.a character at the same time

B.a character to the line

C.the start bit

D.a mark level to the line

(2).The transmitter then send the character, for a duration of T seconds().

A.each bit

B.all bits

C.successive bits

D.a start bit and a character

(3).Finally, the transmitter sends a stop bit at the same level as for one or two bit periods().

A.the space level

B.the mark level

C.the complement of the mark level

D.another character

(4).At the receiving end of an asynchronous serial data link, the receiver().

A.does not monitor the start bit

B.waits until the beginning of the start bit

C.samples the start bit at its center

D.generates a local clock

(5).When the received character has been assembled, its parity().

A.is set to indicate a transmission error

B.is compared with the received character

C.is an error flag

D.may be equal to the received parity