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Question-1. What does VHDL stand for?
Answer-1: VHDL stands for VHSIC Hardware Description Language, where VHSIC means Very High-Speed Integrated Circuit.
Question-2. What is VHDL used for?
Answer-2: VHDL is used to describe and simulate digital systems, such as FPGA and ASIC designs, at various abstraction levels.
Question-3. What are the main components of a VHDL design?
Answer-3: A VHDL design consists of an entity, an architecture, and often a configuration.
Question-4. What is an entity in VHDL?
Answer-4: An entity defines the interface of a digital component, including its inputs and outputs.
Question-5. What is an architecture in VHDL?
Answer-5: An architecture describes the internal behavior or structure of the entity.
Question-6. What are the abstraction levels in VHDL?
Answer-6: VHDL supports three abstraction levels: behavioral, dataflow, and structural.
Question-7. What is a signal in VHDL?
Answer-7: A signal is used to represent connections and communication between components in a design.
Question-8. What is the difference between signals and variables in VHDL?
Answer-8: Signals are used for inter-process communication and have delays, while variables are local to a process and update immediately.
Question-9. How do you declare a signal in VHDL?
Answer-9: Signals are declared in the architecture or process using the signal keyword, e.g., signal clk: std_logic;.
Question-10. What is the std_logic type in VHDL?
Answer-10: std_logic is a single-bit data type that can represent multiple logic states like '0', '1', 'Z', 'U', etc.
Question-11. What is the purpose of libraries in VHDL?
Answer-11: Libraries provide access to pre-defined packages and modules, such as IEEE for standard logic types and arithmetic functions.
Question-12. What is a process in VHDL?
Answer-12: A process is a concurrent construct that describes sequential behavior within a design.
Question-13. How does a process differ from concurrent statements in VHDL?
Answer-13: A process executes sequentially, while concurrent statements describe parallel behavior.
Question-14. What are sensitivity lists in VHDL?
Answer-14: Sensitivity lists define the signals that trigger the execution of a process.
Question-15. What is a testbench in VHDL?
Answer-15: A testbench is a simulation model used to verify the functionality of a VHDL design.
Question-16. What are generics in VHDL?
Answer-16: Generics are parameters that allow customization of a design, such as bit width or timing constants.
Question-17. How do you declare constants in VHDL?
Answer-17: Constants are declared using the constant keyword, e.g., constant clk_period: time := 10 ns;.
Question-18. What is the difference between std_logic and bit?
Answer-18: std_logic supports multiple states, while bit supports only '0' and '1'.
Question-19. What is a component in VHDL?
Answer-19: A component is a reusable design unit that can be instantiated within other designs.
Question-20. How do you instantiate a component in VHDL?
Answer-20: Components are instantiated using the component declaration and port map statement.
Question-21. What is delta delay in VHDL?
Answer-21: Delta delay is a simulation time delay of 0 seconds used to resolve signal assignments in a zero-time context.
Question-22. What is the wait statement in VHDL?
Answer-22: The wait statement suspends a process until a specific condition is met, such as wait for 10 ns;.
Question-23. What is the if-else construct in VHDL?
Answer-23: The if-else construct is used for conditional statements in sequential code, e.g., if a = '1' then b <= '0'; else b <= '1';.
Question-24. What is the case statement in VHDL?
Answer-24: The case statement is a multi-way branching construct used for decision-making based on a value.
Question-25. What are user-defined types in VHDL?
Answer-25: User-defined types are custom data types declared using the type keyword, such as type state is (IDLE, RUNNING);.
Question-26. What is a package in VHDL?
Answer-26: A package is a collection of related declarations, such as types, subprograms, and constants, used to modularize code.
Question-27. What is the port keyword in VHDL?
Answer-27: The port keyword is used to declare input, output, and bidirectional signals in an entity.
Question-28. How does VHDL handle delays?
Answer-28: Delays are modeled using after clauses in signal assignments, e.g., signal <= '1' after 10 ns;.
Question-29. What is the with-select statement in VHDL?
Answer-29: The with-select statement is a concurrent conditional assignment, e.g., with sel select out <= a when "00", b when "01";.
Question-30. How do you perform a for-loop in VHDL?
Answer-30: For-loops are written using for variable in range loop ... end loop;.
Question-31. What are attributes in VHDL?
Answer-31: Attributes are properties of objects, such as signals, that provide additional information, e.g., 'event or 'range.
Question-32. What is the role of the assert statement in VHDL?
Answer-32: The assert statement is used for verification by checking conditions during simulation.
Question-33. What is synthesis in VHDL?
Answer-33: Synthesis is the process of converting VHDL code into hardware logic that can be implemented on FPGAs or ASICs.
Question-34. What is a concurrent signal assignment in VHDL?
Answer-34: A concurrent signal assignment directly assigns a value to a signal based on conditions or expressions.
Question-35. What is a guarded signal in VHDL?
Answer-35: A guarded signal is used in designs with clocked logic and is enabled by a guard condition.
Question-36. What are subprograms in VHDL?
Answer-36: Subprograms include functions and procedures used to encapsulate reusable code.
Question-37. What is the difference between a function and a procedure in VHDL?
Answer-37: A function returns a single value, while a procedure can return multiple values through parameters.
Question-38. What is the difference between simulation and synthesis in VHDL?
Answer-38: Simulation tests the design's functionality, while synthesis converts the design into hardware.
Question-39. What is the purpose of configurations in VHDL?
Answer-39: Configurations define which architecture is used for a specific entity in a design.
Question-40. What is the rising_edge function in VHDL?
Answer-40: The rising_edge function detects a low-to-high transition on a signal, commonly used in clocked designs.
Question-41. How do you model combinational logic in VHDL?
Answer-41: Combinational logic is modeled using concurrent or sequential assignments without memory elements.
Question-42. What is the purpose of reset in VHDL designs?
Answer-42: The reset signal initializes the design to a known state.
Question-43. What are the common VHDL tools?
Answer-43: Common tools include ModelSim, Xilinx Vivado, and Intel Quartus Prime for simulation and synthesis.
Question-44. How do you declare an array in VHDL?
Answer-44: Arrays are declared using the array keyword, e.g., type data_array is array (0 to 7) of std_logic;.
Question-45. What is the generate statement in VHDL?
Answer-45: The generate statement is used to create repetitive hardware structures, such as loops for component instantiation.
Question-46. What is the difference between inertial and transport delays in VHDL?
Answer-46: Inertial delays ignore short pulses, while transport delays simulate signal propagation exactly as described.
Question-47. What is a guarded block in VHDL?
Answer-47: A guarded block uses the guarded keyword for signals controlled by a clock or other condition.
Question-48. What is the purpose of the next statement in VHDL?
Answer-48: The next statement skips the remaining code in a loop iteration and proceeds to the next iteration.
Question-49. How do you perform hierarchical design in VHDL?
Answer-49: Hierarchical design is done by instantiating lower-level components within higher-level designs using component declarations and port maps.
Question-50. What is a signal driver in VHDL?
Answer-50: A signal driver is a source that assigns values to a signal. Multiple drivers are resolved using resolution functions for signals like std_logic.
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