(Regular Logic Implementation Methods) You are to design a converter that maps a 4-bit binary code into a 4-bit Gray code. The 4-bit Gray-code sequence is defined as follows: 0000, 0001, 0011, 0010, 0110, 0111, 0100, 1100, 1101, 1111, 1110, 1010, 1011, 1001, 1000. Give the truth table, and show how to implement this code converter as a ROM circuit and as a PLA circuit.