Parity/Non-Parity Check Essay, Research Paper

Parity/Non-parity Check

Early transmission codes had a serious problem in that a bit

could be lost or gained in transmission because of an electrical

or mechanical failure/ If the loss went undetected, the character

received on the other end of the lime was incorrect.

To Prevent this from happening, a parity check system was

developed. Each character is represented by a byte consisting of

a combination of intelligence bits (seven bits in ASCII and eight

bits in EBCDIC) and an additional bit called a check or parity

bit.

Even parity codes place a check bit with each byte that

contains an uneven number of 1 bits. (Remember that a bit is

either 1 or o). Because the check bit is transmitted only with

characters composed of an uneven number of 1 bits,all characters

transmitted will have n even number of 1 bits. The check bit

is transmitted to and from the computer along with character

code. If a bit is lost (or added) in transmission, the system

will detect its loss. An uneven number of 1 bits received in a

code string composed of even bits will signal an error.

Odd Parity codes add a check bit to code combinations that

have an even number of 1 bits. Thus,all characters transmitted

have an odd number of bits. Odd and even parity care similar in

nature. They are both designed to signal an error in the even

that data are lost or added.