# Implementing Sequential Circuits with VHDL

This set of VHDL written test Questions & Answers focuses on “Implementing Sequential Circuits with VHDL”.

1. A sequential logic can’t be executed by concurrent statements only.
a) True
b) False

2. Which of the following sequential circuit doesn’t need a clock signal?
a) Flip flop
b) Asynchronous counter
c) Shift register
d) Latch

3. The following timing diagram shows ______ flip flop.

a) T flip-flop
b) D flip-flop
c) SR flip-flop
d) JK flip-flop

4. The process used for implementation of sequential logic in VHDL is called ______ process.
a) Sequential process
b) Combinational process
c) Clocked process
d) Unclocked process

5. Why do we need to define clock signal in the sensitivity list of the process?
a) To trigger the statement as soon as there is some event on clock
b) To trigger the clock signal as soon as there is some event on input
c) To trigger the clock signal as soon as there is some event on output
d) To trigger the statement as soon as there is some event on input
.

6. A user has designed JK flip flop by using the VHDL code. The output is continuously switching between 0 and 1. This condition is known as _______
a) Switching condition
b) Master slave condition
c) Race around condition
d) Edge triggered condition

7. Which of the following method is not used to remove the race around condition in a flip flop?
a) Using level triggered flip flop
b) Using master slave flip flop
c) Using edge triggered flip flop
d) All of the above are used to remove the race around

8. Which of the following attribute is generally used in implementation of sequential circuits?
a) ‘STABLE
b) ‘LENGTH
c) ‘LAST_EVENT
d) ‘EVENT

9. Which of the following line is correct for detecting positive edge of a clock?
a) IF (clk’EVENT AND clk = ‘0’)
b) IF (clk’EVENT AND clk = ‘1’)
c) IF (clk’EVENT OR clk = ‘0’)
d) IF (clk’EVENT OR clk = ‘1’)

10. A user doesn’t want to use the IF statement for detecting clock edge. It is possible to do the same by using any other keyword in VHDL.
a) True
b) False