3.6.4.1 Logic Gates. Flashcards
Define a logic gate.
Devices which apply logical operations to one or more Boolean inputs in order to produce a single output.
What name is given to a collection of connected logic gates?
Logic circuit.
What is the purpose of a logic circuit?
To perform more complex operations like binary addition.
How many outputs do logic gates have?
One.
Define the purpose of a truth table.
To show every possible combination of inputs and the corresponding output for a logic gate or logical circuit.
How are the inputs on a truth table labelled?
Alphabetically, starting with A with the output usually labelled as Q.
Outline a NOT gate.
One input and one output.
Output is the opposite of the input.
Truth table has two columns, labelled A and Q.
Outline the Boolean algebra equation for NOT.
_
A = A
Outline an AND gate.
Two inputs, out output.
Output is the product of the inputs.
Only outputs true (1) when or one, or both, inputs are true, otherwise it outputs false.
Outline the Boolean equation for AND.
Q = A x B
Outline an OR gate.
Two inputs, out output.
Input + input = output.
Only outputs false (0) when both inputs are false, otherwise it outputs true.
Outline the Boolean equation for OR.
Q = A + B
Outline a XOR gate.
Aka exclusively or.
Outputs true when strictly one of its inputs are true.
Outputs false when both inputs are true.
Used in the vernam cipher.
Outline the Boolean equation for XOR.
Q = A ⊕ B
Outline a NAND gate.
Aka not and.
Combination of the NOT and AND gates.
Only outputs false (1) when or one, or both, inputs are false, otherwise it outputs
true.
Outline the Boolean equation for NAND.
____
Q = A × B
Outline a NOR gate.
Aka not or.
Combination of NOT and OR.
Both inputs must be false to elicit a positive output.
outline the Boolean equation for NOR.
____
Q = A + B
Outline a full adder.
Three inputs and two outputs, enabling it to input two Boolean values and a carry bit from the previous, less significant operation.
In a full adder, outline what A, B and Cin stand for.
Carry in.
In a full adder, outline what S stands for.
Sum.
In a full adder, outline what Cout stands for.
Carry out.
Define an Edge-triggered D-type flip-flop.
A logic circuit which can be used as a memory unit for storing the value of a single bit.
How many inputs does an Edge-triggered D-type flip-flop have?
Two, one for data and one for clock signal.
How many outputs does an Edge-triggered D-type flip-flop have?
One, which always holds the value of a stored bit.
How is clock signal generated in an How many inputs does an Edge-triggered D-type flip-flop?
Generated by the computer and alternates between 0 and 1 at a set frequency.
The value of the stored bit is set to the value of the data input with each change
of the clock signal
What other purpose does clock signal have?
The clock signal can also be used to synchronise numerous flip-flops when they form part
of a larger system such as a shift register.
