2. PARITY CHECKER / GENERATOR
Arithmetic Operation – determine the sum of the binary bits in a word is odd or even
Even number of 1’s in n-bit data - Even parity = 1111 0000 1111 0011
Odd number of 1’s in n-bit data - Odd parity = 1111 0000 1111 0111
PARITY CHECKER
Ex -OR Gate used to check parity of binary numbers
Reason – produce high outputs when inputs has odd number of one’s
– produce low outputs when inputs has even number of one’s
16 - bit EX - OR gate
= Produce high output – number has odd parity
= produce low output – number has even parity
3. PARITY GENERATION
Odd parity generator produce odd parity output
Consider 8 - bit numbers = X7 X6 -------- X0
Ex : 0100 0001 = even parity
EX – OR Gate = output “0”
Inverter = Output “1”
( Final output = 9 bit = odd parity )
Ex : 0110 0001 = Odd parity
EX – OR Gate = output “1”
Inverter = Output “0”
( Final output = 9 bit = odd parity )
This ckt is called odd parity generator
To get even parity = remove inverter
4. APPLICATION
Due to transients noise & other disturbances = 1 – bit error occur when binary data
transmitted over telephone lines or other communication paths
one way to check error = odd parity generator at transmitting end
= odd parity checker at the receiving end
If no error – receiving data is an odd parity
If error in the data – receiving data will have even parity
Ex : 0100 0011 Odd parity generator = output “0 0100 0011”
pass through telephone lines
Odd parity checker at the receiving end
If no error occur in transmission = odd parity checker produce high output
If one bit error does creep in the transmitted data = odd parity checker produce low
output indicating the received data is invalid
5. IC 74180
14 – pin IC = TTL parity generator – checker
X7 X6 -------- X0 = input data bits = even or odd parity
Pin 3 = even input control the operation
Pin 4 = odd input of the chip
IC 74180 used to detect even parity or odd parity
IC 74180 also used to generate even or odd parity