1. Using building blocks to make bigger circuits
So far we have defined basic building blocks as
Inverter, AND, and OR gates
storage elements (D-Flip-flop)
These building blocks can be used to bigger circuits
We may give them additional functionality
We can either add more inputs or wider inputs, and outputs
Or we may perform a more complex operation
Or both, like multiplexers, decoders, ….
Examples:
3, 4, 5 …. n bit input gates
Or you may have multiple bit data inputs
AND, OR, XOR, STORE, READ n-bit data

2. Making a register C D Q P D0 D1 D2 D3 Clock Q0 Q1 Q2 Q3
Flip-flops can be connected to act as a register
All clock signals are connected together to one clock
All flip-flops get different input, each storing one-bit information
A 4-bit register is shown -- It uses 4 D-FFs
Has a 4 bit inputs and 1 clock and produces 4 bit output C D Q P D0 D1 D2 D3
Clock Q0 Q1 Q2 Q3

3. Making a shift-register
Flip-flops can also be connected to act as a shift register
All clock signals are connected together to one clock
First flip flop gets a new input
Others get input from previous flip-flop
A 4-bit shift register is shown
It has one bit and one clock input and produces 1 bit output D0 C D Q P
Clock Q0 Q1 Q2 Q3

4. Using 1-bit building blocks to make n-bit circuit
Design a 1 bit circuit with proper “glue logic” to use it for n-bits
It is called a bit slice
The basic idea of bit slice is to design a 1-bit circuit and then piece together n of these to get an n-bit component
Previous two examples showed how to use 1-bit components
However, there was no other glue signal or logic
Next, we consider other kind of examples
A half-adder adds two 1-bit inputs
Two half adders can be used to add 3 bits
A 3-bit adder is a full adder B C S A

5. Full adder and multi-bit adder
Two half adders can be used to add 3 bits
n-bit adder can use full adders
n can be arbitrary large
Cout0
Sum0 A0 B0 Ci
Full
Adder
Cout1
Sum1 A1 B1 C1
Cout2
Sum2 A2 B2 C2
Cout3
Sum3 A3 B3 C3 B C S A B C S A
Cout
Sum
Cout
Sum A B C
Full
Adder

6. Glue Logic Normally the glue logic is part of 1-bit adder
A basic building block has
Primary inputs
Primary outputs
Cascading inputs
Cascading outputs
The cascading signals interact directly with the glue logic
Carry in 1-bit adder is a primary as well as a cascading output
A and B are primary inputs
C is a cascading input
Cout is cascading output
S is primary output