Behavioural Modelling

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

1. The most basic form of behavioral modeling in VHDL is _______
a) IF statements
b) Assignment statements
c) Loop statements
d) WAIT statements

2. For any concurrent assignment statement, which of the following is true?
a) The statement is executed once
b) The statement is executed twice
c) The value of left operand is assigned to right operand
d) The statement is executed as many times as the value changes

3. a < = b after 10ns; In this statement the keyword ‘after’ is used for introducing delay.
a) True
b) False

4. Which of the circuit is described by following VHDL code?

USE IEEE.std_logic_1164.all;
ENTITY my_func IS
PORT(x, a, b : IN std_logic;
q : OUT std_logic);
END my_func;
ARCHITECTURE behavior OF my_func IS
q <= a AFTER 10 ns WHEN 0;
         b AFTER 10 ns WHEN 1;
s <= 0 WHEN x = ‘0’ ELSE
        1 WHEN x = ‘1’;
END behavior;

a) AND gate
b) OR gate
c) MUX 2:1
d) DEMUX 1:2

5. The main problem with behavioral modeling is ________
a) Asynchronous delays
b) Simulation
c) No delay
d) Supports single driver only

6. What is the use of simulation deltas in VHDL code?
a) To create delays in simulation
b) To assign values to signals
c) To order some events
d) Evaluate assignment statements

7. VHDL can’t handle multiply driven signals.
a) True
b) False

8. Which function is used to create a single value for multiple driver signals?
a) Resolution function
b) Package
c) Concurrent assignments
d) Sequential assignments

9. Refer to the VHDL code given below, which of the following signal is driven by multiple drivers?

USE IEEE.std_logic_1164.all;
ENTITY function IS
PORT (b, c : IN BIT;
a, d : OUT BIT);
END function;
ARCHITECTURE behavior OF my_func IS
a <= b;
a <= c;
d <= b;
END behavior;

a) d
b) c
c) b
d) a

10. A signal is driven by two signals b and c. How the value of b and c will be resolved to calculate the value of a?
a) By short circuiting both driver
b) By open circuiting one driver
c) By AND operation between two drivers
d) By NOT operation of both drivers

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