How many input lines are there in a ‘Full Adder’?
Combinational Logic circuits are circuits for which the present output depends only on the present input, i.e. there is no memory element to store the past output.
A combinational circuit can have ‘n’ number of inputs and ‘m’ number of outputs as shown:
Full Adder:
The basic block diagram for a Full Adder is as shown:
A Full adder can be realized using two half adders as shown:
A full adder can be implemented using 2 XOR, 2 AND, 1 OR as shown in figure:
The truth table of a full adder logic is:
A |
B |
C |
Cin |
S |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
0 |
1 |
0 |
1 |
0 |
0 |
1 |
0 |
1 |
1 |
1 |
0 |
1 |
0 |
0 |
0 |
1 |
1 |
0 |
1 |
1 |
0 |
1 |
1 |
0 |
1 |
0 |
1 |
1 |
1 |
1 |
1 |
S = A ⊕ B ⊕ C
The Sum output bit of a full adder is given by:
The carry output bit of a full adder is given by:
X1 = AB + BC + AC
Multiplexers:
Number of control lines = log2(number of input lines)
Sequential Circuits: The block diagram shown below explains this:
The memory elements used are flip flops or latches.
Shift Register: A shift register has the capability to store one bit and if another bit is to store, in such situation it deletes the previous data and stores them. There are four kinds of shift registers: