Parity generator and checker circuits are used to detect errors in data transmission. A parity bit is added to data units using even or odd parity rules. Even parity means the total number of 1 bits including the parity bit is even. Odd parity means the total is odd. During transmission, the sender generates parity bits and the receiver checks them to detect errors. Parity can detect single bit errors but not multiple errors or errors in the parity bit itself. Integrated circuits like the 74280 TTL IC contain parity generator and checker functionality to implement error detection during data transmission.

1. PARITY GENERATOR AND
CHECKER

2. • Irregular changes to data, as it is
recorded when it is entered in
memory.
• Different types of parity errors can
require the retransmission of data or
cause serious system errors, such
as system crashes.
Parity error

3. The most common error detection
code used is the parity bit.
A parity bit is an extra bit included
with a binary message to make the
totalnumber of 1's either odd or even.
In case of even parity, the parity bit is
chosen so that the total number of
1's inthe coded message is even.

4. Alternatively, odd parity can be
used in which the total number
of 1's in thecoded message is
made odd.
During transfer of information,
the message at the sending-end
is applied to aparity generator
where the parity pit is generated.

5. Computers can sometimes
make errors when they
transmit data.
Even/odd parity:
Is basic method for detecting
if an odd number of bits has
been switched by accident.

6. The number of 1-bit must add up
to an odd number
Odd parity:

7. Even parity:
The number of 1-bit must add up to an
even number

9. Parity checking uses parity bits to check
that data has been transmitted accurately.
The parity bit is added to every data unit
(typically seven or eight bits) that are
transmitted. The parity bit for each unit is set
so that all bytes have either an odd number
or an even number of set bits.
Parity checker

10. How Parity Checking Works
1. Assume, for example, that two devices are communicating with even
parity (the most common form of parity checking). As the transmitting
device sends data, it counts the number of set bits in each group of
seven bits. If the number of set bits is even, it sets the parity bit to 0; if
the number of set bits is odd, it sets the parity bit to 1. In this way,
every byte has an even number of set bits. On the receiving side, the
device checks each byte to make sure that it has an even number of
set bits. If it finds an odd number of set bits, the receiver knows there
was an error during transmission.
2. The sender and receiver must both agree to use parity checking and
to agree on whether parity is to be odd or even. If the two sides are
not configured with the same parity sense, communication will be
impossible

11. To calculate parity data for two drives, an XOR is performed on their data:
01101101
XOR 11010100
_____________
10111001
The resulting parity data, 10111001, is then stored on Drive 3.
XOR AND XNOR ARE USED GENERALLY TO
CHECK THE PARITY

12. Even parity

13. Odd parity

14. Integrated-Circuit Parity
Generator/Checker
74280 TTL IC logic symbol and Function
Table

15. Parity Generator/Checker
applications:
•One important application of the use of an Exclusive-
OR gate is to generate parity.
•Parity is used to detect errors in transmitted data
caused by noise or other disturbances.
•A parity bit is an extra bit that is added to a data word
and can be either odd or even parity.
•In an even parity system, the sum of all the bits
(including the parity bit) is an even number
In an odd parity system the sum of all the bits must be
an odd number.

16. •The circuit that creates the parity bit at the transmitter
is called the parity generator.
The circuit that determines if the received data is
correct is the parity checker.
•Parity is good for detecting a single bit error only.
•The parity generator and the parity checker can both
be built using Exclusive-OR gates.

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