IF Statement

VHDL

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

1. What kind of statement is the IF statement?
a) Concurrent
b) Sequential
c) Assignment
d) Selected assignment

2. Which of the following keyword is not associated with IF statement?
a) ELSE
b) THEN
c) ELSIF
d) WHEN

3. Which of the following represents the correct order for keywords?
a) IF, THEN, ELSIF, THEN, ELSE
b) IF, ELSE, THEN, ELSIF, THEN
c) IF, ELSIF, THEN, ELSE, THEN
d) IF, THEN, ELSE, THEN, ELSIF

4. What is the correct syntax for defining an IF statement?
a)

    IF (condition) THEN
    statements;
    ELSIF (condition) THEN
    statements;
    ….;
    ELSE (condition) THEN
    statements;
    END IF;

b)

    IF (condition) THEN
    statements;
    ELSIF (condition) THEN
    statements;
    ….;
    ELSE 
    statements;
    END IF;

c)

    IF (condition) THEN
    statements;
    ELSIF (condition) THEN
    statements;
    ….;
    ELSE (condition)
    statements;
    END IF-ELSE;

d)

    IF (condition) THEN
    statements;
    ELSIF (condition) THEN
    statements;
    ….;
    ELSE 
    statements;
    END IF-ELSE;

5. If the condition of IF statement is an expression, then what should be the type of the result of the expression?
a) Bit
b) Std_logic
c) Boolean
d) Integer

6. In the following lines, what should be the value of signal y, if a and b both are at logic high?

PROCESS (a, b)
BEGIN
IF( a XOR b <=’1’)
y <= ‘1’;
ELSIF (a AND b <= ‘0’)
y &lt;= a;
ELSE
y &lt;= ‘0’;
END IF;
END PROCESS;

a) a
b) b
c) 0
d) 1

7. It is possible to use nested IF in VHDL.
a) True
b) False

8. Which of the following condition has topmost priority?
a) IF
b) ELSIF
c) ELSE
d) THEN

9. What logic is described in the following logic?

PROCESS (a, b)
IF (a = ‘1’ AND b = ‘0’ OR a= ’0’ AND b = ‘1’) THEN
y &lt;= ‘1’;
ELSIF (a = ‘1’ AND b= ‘1’) THEN
y &lt;= ‘0’;
ELSE
 y &lt;= ‘0’;
END IF

a) EXOR
b) EXNOR
c) AND
d) NOR

10. One IF statement can have multiple ___________
a) IF
b) ELSIF
c) ELSE
d) CASE

11. More than one sequential statement can exist between each statement part.
a) True
b) False

12. If a user gets an error at the time of simulation which is “ the IF statement is illegal” what could be the reason?
a) Using IF statement in architecture body
b) Using IF statement without ELSE
c) Using multiple ELSE statements
d) Using concurrent assignment in the IF

13. In a clocked process, IF statement is used to __________
a) To run statements sequentially
b) To use concurrent assignment within process
c) To detect the clock signal
d) To implement sequential circuit

14. What will be the output in the following code?

ARCHITECTURE my_logic OF my_design IS
BEGIN
a &lt;= 1;
b &lt;= 1;
PROCESS (a, b)
BEGIN
IF (a AND b = 1) THEN
output &lt;= a;
ELSIF (a OR b = 1) THEN
output &lt;= b;
ELSE
output &lt;= 0;
END IF;
END PROCESS;
END my_logic;

a) 0
b) 1
c) b
d) a

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