106-3 Parity Generator / Checker Electrical noise in the transmission of binary information can cause errors.0101 -> 0100 (the electrical noise present on the line during the transmission of the LSB may change 1 to 0)Parity can detect these types of errors.Receiving device can signal an error condition or ask the transmitting device to retransmit.the electrical noise present on the line during the transmission of the LSB may change 1 to 0At transmitting side10
11Parity systems Adds a bit to the binary information Odd parity systems 4-bit system requires a 5th bit, an 8-bit system needs a 9th bit.Odd parity systemsThe parity bit that is added must make the sum of all bits odd.Even parity systemsThe parity bit that is added must make the sum of all bits even.
12Parity systems Parity generator Parity checker the circuit that creates the parity bitParity checkerDetermines if the received string is of the right parity on the receiving endThe type of parity system and the location of parity bit (next to MSB or LSM) must be agreed on beforehand.
13Odd parity generator/checker This scheme only detects errors that occur to 1 bit.The likelihood of 2 bits being affected is highly unusual.11
17Integrated-Circuit Parity Generator/Checker 74280 TTL IC logic symbol and Function Table15
18Parity-Error Detection System 8-bit even-parity computer configuration. SumE is HIGH if the sum is even. The generated parity bit should be taken from the Odd output because we want the sum of all 9 bits send out to be EVEN.Low means no error, So the Odd output of the checker at the receiver side is used.17
19Parallel Binary Comparator 1 -> match (two input string are exactly equal)
20Controlled InverterComplement an entire string by some control signal.19
21Discussion PointDoes the circuit below function as an even or odd parity generator?xor 1 = 0 0nxor 0 = 1 Odd parity generator21
22SummaryThe exclusive-OR gate provides a HIGH output if one input or the other input, but not both, is HIGH.The exclusive-NOR gate outputs a HIGH if both inputs are HIGH or if both inputs are LOW.24
23SummaryA parity bit is commonly used for error detection during the transmission of digital signals.Exclusive-OR and exclusive-NOR gates are used in applications such as parity checking, binary comparison and controlled complementing circuits.FPGAs can be used to implement circuits containing the exclusive gates.25