**RT-level combinational components:-**

To reduce the complexity in digital logic, combinational components are used, which are more powerful than logic gates.

Such combinational components are called register-transfer, or RT level components.

The different types of combinational components are

1.Multiplexor

2.Decoder

3.Adder

4.Comparator

5.Arithmetic-Logic Unit (ALU) and

6.Shift register

1.Multiplexer:-

A multiplexer sometimes called a selector, allows only one of its data input I_{m} to pass through to the output "O". Thus

multiplexer acts much like a railroad switch, allowing only one of multiple input tasks to connect to a single output track.

2.Decoder:-

A decoder converts its binary input "I" into a one-hot output "O". "One-hot" means that exactly one of the output lines can be 1 at a given time.

3.Adder:-

An adder adds two n-bits binary inputs A and B, generating on n-bit output sum along with an output carry.

4.Comparator:-

A comparator compares two n-bit binary inputs "A" and "B", generating outputs that indicate whether A is less than, equal to or greater than B.

5.Arithmetic Logic Unit:-

An arithmetic logic unit (ALU) can perform a variety of arithmetic and logic functions on its n-bit inputs A and B.

6.Shift register:-

An n-bit input "I" can be shifted left or right and then output to an output "o".

**RT-level sequential components:-**

1.Register:-

A register stores n-bits from its n-bits data input "I", with those stored bits appearing at its output "Q".

2.Shift register:-

A shift register stores n-bits, but these bits cannot be stored in parallel. Instead, they must be shifted into the register serially, meaning one bit per clock edge.

A shift register has a 1-bit data input I, and at least two control inputs clock and shift.

3.Counter:-

A counter is a register that can also increment, meaning add binary 1, to its stored binary value. A counter has a clear input, which resets all stored bits to "o", and a count input which enables incrementing on each clock edge.

A counter often also has a parallel load data input and associated load control signal.

A common counter feature is both up and down counting or incrementing and decrementing, requiring an additional control input to indicate the count direction.

These control inputs can be either

1.Synchronous

2.Asynchronous

An synchronous input value only has an effect during a clock edge. An asynchronous inputs value effects the circuit independent of the clock.