1. ACOE161Digital Circuit Design1 Design Of Combinational Logic Circuits

2. ACOE161Digital Circuit Design2 Design of combinational digital circuits Steps to design a combinational digital circuit: –From the problem statement derive the truth table –From the truth table derive the unsimplified logic expression –Simplify the logic expression –From the simplified expression draw the logic circuit Example: Design a 3-input (A,B,C) digital circuit that will give at its output (X) a logic 1 only if the binary number formed at the input has more ones than zeros.

3. ACOE161Digital Circuit Design3 Design of combinational digital circuits (Cont.) Example: Design a 4-input (A,B,C,D) digital circuit that will give at its output (X) a logic 1 only if the binary number formed at the input is between 2 and 9 (including).

4. ACOE161Digital Circuit Design4 Design of combinational digital circuits (Cont.) Example: Design a 4-input (A,B,C,D) digital circuit that will give at its output (X) a logic 1 only if the binary number formed by the inputs (AB) is greater or equal to the binary number formed by the inputs (CD).

5. ACOE161Digital Circuit Design5 Tutorial: Design a 4-input (A,B,C,D) digital circuit that will give at its output a binary number equal to the sum of the binary numbers formed by the inputs (AB) and (CD).

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7. ACOE161Digital Circuit Design7 Tutorial: Design a 4-input (A,B,C,D) digital circuit that will give at the output: –X a logic 1 if the binary number formed by the inputs (AB) is greater than (CD). –Y a logic 1 if the binary number formed by the inputs (AB) is less than (CD). –Z a logic 1 if the binary number formed by the inputs (AB) is equal to (CD).

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9. ACOE161Digital Circuit Design9 Homework: Design a 4-input (A,B,C,D) digital circuit that will give at the output: –X a logic 1 if in the binary number formed at the inputs there are more zeros than ones. –Y a logic 1 if in the binary number formed at the inputs there are less zeros than ones. –Z a logic 1 if in the binary number formed at the inputs there equal zeros and ones.

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11. ACOE161Digital Circuit Design11 Homework: Design a 4-input (A,B,C,D) digital circuit that will give at its output a binary number equal to the product of the binary numbers formed by the inputs (AB) and (CD).

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13. ACOE161Digital Circuit Design13 Don’t Care Conditions In many application it is known in advance that some of the input combinations will never occur. These combinations are marked as “Don’t Care Conditions” and are used as either zero’s or one’s so that the application is implemented with the most simplified circuit. Example: Simplify the logic expression X(A,B,C,D) with the don’t care conditions d(A,B,C,D).

14. ACOE161Digital Circuit Design14 Don’t Care Conditions: Examples

15. ACOE161Digital Circuit Design15 Homework: Design a digital circuit that has as input a 1-digit Binary Coded Decimal (BCD) number. The circuit must give at its output a binary number equal to the absolute value of (2M – 5), where M is the number formed at the input.

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