Exp (4)
PARITY CHECKERS
AIM:- to understand the operation of parity checkers
Theory:- errors can occur as digital codes being transferred from one point to another within a digital system . many systems ,however , employ a parity bit as a means of detecting a bit error .binary information is in group of bits called words . A word always contains either an even or odd number of 1 s . A parity bit is attached to the group of information bits in order to make the total number of 1 s always even or always odd . an even parity bit makes the total number of 1 s even and an odd parity bit makes the total odd.
A given system operates with even or odd parity , but not both , for instance if a system operates with even parity , a check is made on each group of bits received to make sure that the total number of 1 s in that group is even . if there is an odd number of 1 s , an error has occurred
The parity bit can be attached to the code group at either the beginning or the end , depending on system design , notice that the total number of 1 s , including the parity bit is always even for even parity and always odd for odd parity .
A truth table of even parity and odd parity is shown below :
|
A
|
B
|
C
|
Even parity Pe
|
Odd parity Po
|
|
0
|
0
|
0
|
0
|
1
|
|
0
|
0
|
1
|
1
|
0
|
|
0
|
1
|
0
|
1
|
0
|
|
0
|
1
|
1
|
0
|
1
|
|
1
|
0
|
0
|
1
|
0
|
|
1
|
0
|
1
|
0
|
1
|
|
1
|
1
|
0
|
0
|
1
|
|
1
|
1
|
1
|
1
|
0
|
From the truth table :-
Pe = AB`C`+ A`BC` + A`B`C + ABC
= C`[AB`+A`B] + C[AB + A`B`] let Z= AB`+A`B
= C`Z+CZ` Z`= AB+A`B`
Pe = C ± Z ……….1
Po = A`B`C` + ABC`+ AB`C + A`BC
= C` [A`B`+ AB ] + C [ AB`+A`B]
= C`Z`+ CZ
Po = C ± Z ………….2
From eq(1) , (2) we can draw the logic diagram As in fig.(1) , fig (2)
C
Fig(1) a
Fig(1) b
l
Fig(2) a
PROCEDURE
1- connect the circuit as shown in fig(1) b
2- state the truth table.
3- Connect the circuit as shown in fig(2) b
4- State the truth table
5- Design an even parity and an odd parity for four input data.
6- Simplify the circuit and connect it
7- State the truth table of the circuit.
DISCUSSION
1-Assign the proper even parity bit to the following code words
1010,111000,100011100101and 1011010111111
2- An odd parity system receives the following code words
110011,11011110100,1100010101010 determine which ones , if any ,are in error.
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .