Consider that three input message along with even parity bit is generated at the transmitting end. These 4 bits are applied as input to the parity checker circuit, which checks the possibility of error on the data. Since the data is transmitted with even parity, four bits received at circuit must have an even number of 1s.
If any error occurs, the received message consists of odd number of 1s. The output of the parity checker is denoted by PEC (Parity Error Check).
The below table shows the truth table for the Even Parity Checker in which PEC = 1 if the error occurs, i.e., the four bits received have odd number of 1s and PEC = 0 if no error occurs, i.e., if the 4-bit message has even number of 1s.
K-Map for the even parity checker
The above logic expression for the even parity checker can be implemented by using three Ex-OR gates as shown in figure. If the received message consists of five bits, then one more Ex-OR gate is required for the even parity checking.