Logic Circuits Flashcards

All 8 cards in this deck

What shape is the AND gate symbol in a logic diagram?

A 'D' shape — a flat vertical edge on the left for the inputs and a semicircular curve on the right for the output.

What shape is the OR gate symbol in a logic diagram?

A curved (concave) left-hand edge with two curved sides meeting at a point on the right.

What shape is the NOT gate symbol in a logic diagram?

A triangle pointing right with a small circle (bubble) on its output; it has only one input.

What is a logic circuit?

Two or more logic gates connected together, where the output of one gate can become an input to another.

What are the steps to complete a truth table for a circuit with two gates?

e.g. $Q = A . \overline{B}$

1. List every input combination of A and B: 00, 01, 10, 11.

2. Add a column for the first gate: $\overline{B}$ = 1, 0, 1, 0.

3. Apply the final gate (AND) to get Q: 0, 0, 1, 0 (so Q = 1 only when A = 1 and B = 0).

What are the steps to correct a logic circuit that produces the wrong output?

e.g. a circuit gives $Q = A + B$ but $Q$ should be 1 only when both inputs are 1

1. Write the Boolean expression for the circuit as drawn: $Q = A + B$
2. Write the expression the scenario or truth table requires: $Q = A . B$
3. Change the gate(s) that differ: replace the OR gate with an AND gate.

How do you edit a logic diagram whose output is correct except that every value is the opposite of the one required?

e.g. the diagram gives 1 for every row where the truth table needs 0

Add a NOT gate to the output of the final gate.

It inverts every output, so 1 becomes 0 and 0 becomes 1.

What shape is the XOR gate symbol in a logic diagram?

The OR gate shape with an extra curved line drawn across its inputs, just to the left of the curved input edge.