THEORY EXAMINATION (SEM–VIII) 2016-17 DIGITAL SYSTEMS USING VHDL

SECTION – A

Explain the following (Short Answer Type)

Combinational circuits are digital circuits whose output depends only on present input values, such as adders and multiplexers. Sequential circuits depend on both present inputs and previous outputs because they include memory elements like flip-flops.

VHDL is a hardware description language used for designing digital systems. Its applications include simulation, modeling, and synthesis of digital circuits. Its advantages include portability, reusability, and support for complex system design.

Structural modeling in VHDL describes circuits by connecting smaller components. For example, a full adder can be created by connecting two half adders and an OR gate.

Generic parameters in VHDL are used to define constants that can be changed during instantiation, making designs flexible and reusable.

A 4:2 encoder converts four input lines into two output lines using behavioral modeling, which describes system functionality using sequential statements.

Digital design has three abstraction levels: behavioral level, register transfer level, and structural level. These levels help designers describe systems from high-level functionality to hardware implementation.

Lexical elements are basic building blocks of VHDL such as identifiers and keywords. Signals represent wires that carry data, while variables store temporary values inside processes.

Inertial delay is a type of delay in VHDL that ignores short pulses and represents physical circuit delay.

A 2:4 multiplexer selects one of two input lines and sends it to four outputs depending on select signals, implemented using structural modeling.

Binding alternatives define how components are connected to actual hardware entities during compilation.

Questions (Section A)

Differentiate between combinational and sequential circuits.

Write applications of VHDL.

What are generic parameters?

Define lexical elements, signals, and variables.

What is inertial delay?

SECTION – B

Attempt any five (Long Answer Type)

Delta delay is a simulation concept that represents very small time steps used to update signal values. Transaction appending rules define how signal changes are scheduled in simulation.

Sequential modeling describes digital systems using processes and sequential statements. Attributes provide additional information about signals such as timing and value changes.

The basic structure of VHDL includes entity declaration, architecture body, and configuration. A multiplexer can be implemented using conditional statements within architecture.

A SIPO (Serial-In Parallel-Out) shift register accepts serial input data and provides parallel output after shifting operations. It is implemented using flip-flops.

Synthesis rules define how VHDL code is converted into hardware. Designers must follow specific coding styles to ensure successful hardware implementation.

A D flip-flop stores one bit of data and changes its output based on clock signals. It is widely used in memory and registers.

Guarded signal assignment ensures signal changes occur only when certain conditions are satisfied.

Inertial delay ignores short pulses, while transport delay passes all signal changes regardless of duration.

Questions (Section B)

Explain delta delay in VHDL.

What is sequential modeling?

Explain the structure of VHDL.

What is a SIPO shift register?

Differentiate between inertial and transport delay.

SECTION – C

Attempt any two (Detailed Explanation)

Testing in digital design ensures circuits function correctly. It includes techniques such as functional testing, fault detection, and debugging. Design test issues include test coverage, cost, and reliability.

RAM (Random Access Memory) is a storage device used in digital systems. Behavioral VHDL code describes RAM operations such as read, write, and address selection.

Floating-point multiplication involves multiplying mantissas, adding exponents, and normalizing the result. It is used in scientific and engineering calculations.

Questions (Section C)

Explain testing in digital design.

Write behavioral VHDL code for RAM.

Explain floating-point multiplication logic.