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Draw the logic circuit to decode the following binary number (0001, 0101, 0111, 1000, 1010, 1100…

Computer Science20255 marksDrawing
Draw the logic circuit to decode the following binary number (0001, 0101, 0111, 1000, 1010, 1100, 1110, 1111) to its hexadecimal equivalents. Also state the Hexadecimal equivalents of the given binary numbers.

Answer

Answer

Official answer key
The 4-bit binary inputs are labelled A, B, C, D (A = MSB ... D = LSB). Each input line feeds a buffer (true form) and a NOT gate (complemented form). Each given binary number is decoded by one 4-input AND gate, taking the true or complemented form of A, B, C, D as required so the gate outputs 1 only for that exact combination: 0001 -> A'.B'.C'.D -> output labelled 1 0101 -> A'.B.C'.D -> output labelled 5 0111 -> A'.B.C.D -> output labelled 7 1000 -> A.B'.C'.D' -> output labelled 8 1010 -> A.B'.C.D' -> output labelled A 1100 -> A.B.C'.D' -> output labelled C 1110 -> A.B.C.D' -> output labelled E 1111 -> A.B.C.D -> output labelled F Hexadecimal equivalents: 0001 = 1, 0101 = 5, 0111 = 7, 1000 = 8, 1010 = A, 1100 = C, 1110 = E, 1111 = F.
A 4-to-16 line decoder built from eight 4-input AND gates. Four input lines A, B, C, D each also feed a NOT gate to make A', B', C', D' available. Each AND gate is wired to the correct combination of true/complemented literals (as listed above) so its output is 1 only for its designated 4-bit code; the 8 AND-gate outputs are labelled with their hexadecimal equivalents 1, 5, 7, 8, A, C, E, F.
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From ISC 2025 Specimen Computer Science Paper 1, question 5(i).