VHDL Questions and Answers – RTL Simulation

This set of VHDL Multiple Choice Questions & Answers (MCQs) focuses on “RTL Simulation”.

1. What does RTL in digital circuit design stand for?
a) Register transfer language
b) Register transfer logic
c) Register transfer level
d) Resistor-transistor logic

Explanation: RTL in digital circuit design stands for register transfer level, used in HDL. Register transfer language is a type of intermediate representation close to assembly language. Resistor-transistor logic is used in BJTs as switching devices. Register transfer logic is used in state machine designs.

2. RTL is a design abstraction of what kind of circuit?
a) Asynchronous digital circuit
b) Synchronous digital circuit
c) Asynchronous sequential circuit
d) Analog circuit

Explanation: RTL is a design abstraction that shapes a synchronous digital circuit with reference to digital signals that flow between hardware registers and the logical operations are carried out on those signals.

3. RTL is used in HDL to create what level of representations in the circuit?
a) High-level
b) Low-level
c) Mid-level
d) Same level

Explanation: RTL is used in HDL for creating HIGH-LEVEL of representations in the circuit, from which lower-level of representations can be derived. Designing at the RTL level is a representative practice in modern digital design.

4. RTL mainly focuses on describing the flow of signals between ________
a) Logic gates
b) Registers
c) Clock
d) Inverter

Explanation: RTL focuses on describing the flow of signals between registers. There is a regularly repeated path of logic from the output of the register to its input, that is the reason it is called register transfer level.

5. Which flip-flop is usually used in the implementation of the registers?
a) D flip-flop
b) S-R flip-flop
c) T flip-flop
d) J-K flip-flop

Explanation: Registers are generally implemented as D flip-flops because connection for the shift register is the simplest with D flip-flop, as there is a single data input in it. The flip-flop also stores the output of whatever logic is applied to its data input as long as the clock input is high.
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6. Which of the following tool performs logic optimization?
a) Simulation tool
b) Synthesis tool
c) Routing tool
d) RTL compiler

Explanation: Synthesis tool performs logic optimization in RTL by converting high-level description of the design circuit into an optimized gate level representation by the use of basic logic gates like and, or, nor, etc.

7. RTL is a combination of both combinational and sequential circuits.
a) True
b) False

Explanation: RTL is a combination of both combinational and sequential circuits. Combinational logic performs all the logical operations in the circuit and it typically consists of basic logic gates and registers make synchronized sequential logic.

8. Setup time is the time required for input data to settle after the triggering edge of the clock.
a) True
b) False

Explanation: The time required for an input data to settle BEFORE the triggering edge of the clock is called the setup time. It is measured with respect to active clock pulse edge only.

9. Hold time is the time needed for the data to ________ after the edge of the clock is triggered.
a) Decrease
b) Increase
c) Remain constant
d) Negate

Explanation: Hold time is the time needed for the data to remain constant after the edge of the clock is triggered. Data must remain stable, if the incorrect data is latched then, it leads to hold violation.

10. Simulator enters in which phase after the initialization phase?
a) Execution phase
b) Compilation phase
c) Elaboration phase
d) Simulation phase

Explanation: Simulator enters in execution phase after the initialization phase, the actual simulation of the behaviour of the design takes place in the execution phase. Each simulation process in the active queue is taken out and executed until it suspends.

11. Conversion of RTL description to Boolean _______ description is a function of the translation procedure in the synthesis process.
a) Optimized
b) Unoptimized
c) Translation
d) PLA format

Explanation: Conversion of RTL description to Boolean unoptimized description is a function of translation procedure in the synthesis process. The logic synthesis tool converts the description to an unoptimized, intermediate, internal representation.

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