6.4 Logic gates Flashcards
What do truth tables do?
A truth table shows every possible combination of inputs and the corresponding output for a logic gate or logic circuit.
Describe the NOT gate. Describe its symbol?
The NOT gate has one input and one output. The gates output is always the opposite of the input. The symbol is a triangle point to the right with a circle at the point.
Describe the AND gate. Describe its symbol?
The AND gate has two inputs and outputs 1 if both inputs are also 1. It looks like a D shape with 2 inputs on the left and 1 output on the right.
Describe the OR gate. Describe its symbol?
The OR gate has two inputs. It will result in a 1 if either inputs are 1. It looks like a shield with 2 inputs on the left and 1 output on the right.
Describe the XOR gate. Describe its symbol?
It is known as exclusive or and has two inputs. It will only output 1 if either of the 2 inputs are 1 not both. It looks like a shield but with a line at the two inputs.
Describe the NAND gate. Describe its symbol?
NAND is short for NOT AND. It is an AND gate combine with a NOT gate. It has the opposite outputs as the AND gate. It looks like a D with a circle at the output.
Describe the NOR gate. Describe its symbol?
NOR is short for NOT OR. It is the combination of the OR gate with a NOT gate. It has the opposite outputs of an OR gate. It looks like a shield with a dot at the output.
What is an adder?
logic circuit that can be used to add boolean values together.
2 types of adder.
Full adder and half adder.
What is a half adder?
Two inputs, two outputs and two logic gates
Used to add two boolean values
Inputs labelled A and B
Outputs labelled S and C
for sum and carry
Draw a half adder
Two inputs A and B go through a XOR gate and separately an AND gate
Output at S and C
What is a full adder?
3 inputs labelled A , B and C(in) for carry in
Two outputs labelled S for sum and C(out) for carry out
Can input two boolean values and a carry bit carry bit taken from previous less significant operation.
Draw a full adder
3 inputs A, B and C(in)
A and B go through XOR and an AND gate separately.
The XOR output of A and B goes through a XOR gate with C(in) to output at S
The XOR output with A and B also goes through an AND gate with C(in) which then goes through an AND gate with A and B. These two outputs are outputted at C(out)
Describe the functionality of an Edge-triggered D type flip-flop
Can be used as a memory unit
Stores the value of a single bit
Two inputs one for data and one for a clock signal
One output which holds the value of the stored bit
The value of the stored bit is set with each change of clock signal
Describe the functionality of the clock signal in an edge-triggered D type flip flop
Is generated by the computer
Alternates between 1 and 0
Alternates at a set frequency
Can be used to synchronise numerous flip-flops when they form part of a larger system
