Refer to Table 4.8 in the textbook for the truth table of priority encoder.
Change the priority to the bit from bit.
Prepare a truth table for the priority encoder with the highest priority given to .
The Table 1 shows that the has the highest priority. W represents the valid condition. If one of the inputs is 1, then the valid (W) will be 1. If the valid (W) is 0, then outputs X and Y will have don’t care.
Draw the Karnaugh map for . Substitute 0 and 1, for the don’t care terms.
The expression for the output is,
Thus, the expression for the output is .
Draw the Karnaugh map for . Substitute 0 and 1, for the don’t care terms.
The expression for the output is,
Thus, the expression for the output is .
Draw the Karnaugh map for . Substitute 0 and 1, for the don’t care terms.
The expression for the output is,
Thus, the expression for the output is .
Therefore, four input priority encoder circuit has been implemented with input having the highest priority.