# Implementing Combinational Circuits with VHDL – 2 MCQ’s

This set of VHDL Multiple Choice Questions & Answers (MCQs) focuses on “Implementing Combinational Circuits with VHDL – 2″.

1. Why we need to include all the input signals in the sensitivity list of the process?

a) To monitor the output continuously

b) To monitor the input continuously

c) To make the circuit synthesizable by EDA tools

d) No special purpose

2. If only two bit vectors are allowed to use in the VHDL code, then how many number of MUX will be required to implement 4 to 1 MUX?

a) 1

b) 2

c) 3

d) 4

3. The process statement used in combinational circuits is called ______ process.

a) Combinational

b) Clocked

c) Unclocked

d) Sequential

4. A package is designed called mux4to1_package, in which a component called mux4to1 is defined, which is a 4 to 1 multiplexer. Now a user wants to design a 16 to 1 MUX by using the same component only, how many times he needs to use the PORT MAP statement?

a) 2

b) 3

c) 4

d) 5

5. The given code represents a convertor. Which kind of convertor it is?

ENTITYconvertISPORT(b:INSTD_LOGIC_VECTOR(3DOWNTO0); x :OUTSTD_LOGIC_VECTOR(7DOWNTO0));ENDconvert;ARCHITECTUREconvertorOFcovertISBEGINPROCESS(b)BEGINCASEbISWHEN“0000” => x <= “1111110”;WHEN“0001” => x <= “0110000”;WHEN“0010” => x <= “1101101”;WHEN“0011” => x <= “1111001”;WHEN“0100” => x <= “0110011”;WHEN“0101” => x <= “1011011”;WHEN“0110” => x <= “1011111”;WHEN“0111” => x <= “1110000”;WHEN“1000” => x <= “1111111”;WHEN“1001” => x <= “1110011”;WHENOTHERS=> x <= “0000000”;ENDCASE;ENDPROCESS;ENDconvertor;

a) Gray to BCD

b) 7 segment to BCD

c) BCD to gray

d) BCD to 7 segment display

6. In designing a 2 to 1 demultiplexer with input d, output y and select line s, which of the following is a correct process statement?

a) PROCESS(d)

b) PROCESS(d(0), d(1), s)

c) PROCESS(d(0), d(1))

d) PROCESS(d, s, y)

7. What is the function of the below code?

ENTITYmy_logicISPORT(din : STD_LOGIC_VECTOR(7DOWNTO0); Count : STD_LOGIC_VECTOR(3DOWNTO0));ENDmy_logic;ARCHITECTUREbehaviorOFmy_logicISBEGINCount <= “0000”PROCESS(din)BEGINL1:FORiIN0TO7LOOPIF(din(i) = ‘1’)THENCount = count+1;ELSENEXTL1;ENDLOOP;ENDPROCESS;ENDbehavior;

a) To count number of ones in the given data

b) To count number of zeroes in the given data

c) To reverse the order of given data

d) To perform binary multiplication of two data inputs

8. In the combinational process, the use of output signal in the sensitivity list is illegal.

a) True

b) False

9. A parity generator is a combinational circuit and is designed by using a combinational process.

a) True

b) False

10. What will be the value of count output, if the data din is 11001111?

ENTITYmy_logicISPORT(din : STD_LOGIC_VECTOR(7DOWNTO0); Count : STD_LOGIC_VECTOR(3DOWNTO0));ENDmy_logic;ARCHITECTUREbehaviorOFmy_logicISBEGINCount <= “0000”PROCESS(din)BEGINL1:FORiIN0TO7LOOPIF(din(i) = ‘1’)THENCount = count+1;ELSENEXTL1;ENDLOOP;ENDPROCESS;ENDbehavior;

a) 6

b) 0110

c) 2

d) 0010

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