CHAPTER08 QUESTIONS MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) A logic circuit which determines if one input is equal to another is called A) a comparator. B) an adder. C) a multiplexer. 2) A priority encoder means that A) the lowest priority goes first. C) priority is programmed into the device. D) a decoder. B) the highest input has priority. D) the lowest input has priority. 1) 2) 3) What is the output of the 74147 Decimal-to BCD Encoder when input I8 is LOW? A) A3 -A0 = 1100 B) A3 -A0 = 1110 C) A3 -A0 = 0111 D) A3 -A0 = 0101 3) 4) A circuit which converts some binary code into a singular active output representing its numerical value is a A) demultiplexer. B) comparator. C) decoder. D) multiplexer. 4) 5) Which input to a 7442 BCD-to-Decimal decoder will cause output 6 to go LOW? A) A3 -A0 = 0110 B) A3 -A0 = 0011 C) A3 -A0 = 1100 D) A3 -A0 = 1001 5) 6) A VHDL comparator uses a(n) ________ comparison A) IF-THEN-ELSE B) PLA C) SPLD D) IF-THEN 6) 7) When data input I6 of a 74148 octal-to-binary encoder is active, the data output is A) A0 = 0 B) A0 = 0 C) A0 = 0 D) A0 = 1 A1 = 1 A1 = 0 A1 = 1 A1 = 0 A2 = 0 A2 = 1 A2 = 1 A2 = 0 7) 8) What is binary value of BCD number: 0001 0001 1000 (118)? A) 0001 0001 0110 B) 0001 0010 0011 C) 0111 0111 8) D) 0111 0110 9) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 0001 and B = 0100? A) A<B is 0 B) A<B is 0 C) A<B is 1 D) A<B is 0 A=B is 1 A=B is 1 A=B is 0 A=B is 0 A>B is 1 A>B is 0 A>B is 0 A>B is 1 9) 10) Why are LED displays often multiplexed? A) because the data is not available for all displays at once B) so that multiplexers can be used C) to save power D) to save time 10) 11) What is the output of the 74147 Decimal-to-BCD Encoder when input I5 is LOW? A) A3 -A0 = 1010 B) A3 -A0 = 1100 C) A3 -A0 = 0010 D) A3 -A0 = 0101 11) 1 12) If the inputs of a 74139 dual four-line demultiplexer are as shown below, which output is correct? Ea = data A0a = 1 12) Eb = data A0b = 0 A1a = 0 A1b = 0 A) 1a = data 0b = data B) 0a = data 1b = data C) 2a = data 2b = data D) 1a = data 1b = data 13) Output 6 of a 74138 octal decoder is selected when it is enabled by a data input of A) A0 = 0 B) A0 = 1 C) A0 = 0 D) A0 = 1 A1 = 0 A1 = 1 A1 = 1 A1 = 0 A2 = 1 A2 = 0 A2 = 1 A2 = 0 13) 14) How many possible combinations can a 5-bit Gray Code have? A) 32 B) 20 C) 5 14) D) 16 15) In order to select data input I1 of a 74151 eight-line multiplexer, the select inputs must be A) E = 1 S0 = 0 S1 = 0 B) E = 0 S0 = 1 S1 = 0 C) E = 0 S0 = 1 S1 = 1 D) E = 0 S0 = 1 S1 = 0 S2 = 1 S2 = 1 S2 = 0 S2 = 0 15) 16) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 0110 and B = 1010? A) A < B is 0 B) A < B is 1 C) A < B is 1 D) A < B is 0 A > B is 0 A = B is 0 A = B is 0 A = B is 1 A > B is 1 A > B is 0 A > B is 1 A > B is 0 16) 17) Weighting factors are used in A) priority encoders. C) BCD-to-Binary Conversion. 17) B) decoders. D) multiplexers. 18) A multiplexer is a device which A) generates an encoded output from a numeric input. B) converts some code into a recognizable number or character. C) routes a single data input onto one of several data outputs. D) selects one of several inputs to be placed onto one output line. 19) A device which determines which of two numbers is greater is a A) decoder. B) counter. C) multiplexer. 18) D) comparator. 20) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 0100 and B = 0010? A) A<B is 0 B) A<B is 1 C) A<B is 1 D) A<B is 0 A=B is 1 A=B is 1 A=B is 0 A=B is 0 A>B is 0 A>B is 0 A>B is 0 A>B is 1 2 19) 20) 21) When data input I4 of a 74148 octal-to-binary encoder is active, the data output is A) A0 = 0 B) A0 = 1 C) A0 = 0 D) A0 = 1 A1 = 1 A1 = 1 A1 = 0 A1 = 0 A2 = 0 A2 = 0 A2 = 0 A2 = 0 21) 22) Which device is an application of sum-of-products (SOP) logic? A) demultiplexer B) counter C) multiplexer 22) D) comparator 23) If the inputs of a 74139 dual four-line demultiplexer are as shown below, which output is correct? Ea = HIGH A0a = 1 23) Eb = data A0b = 0 A1a = 1 A1b = 1 A) 3b = data B) 0b = data C) 1a = data D) 3a = HIGH 24) When data input I5 of a 74148 octal-to-binary encoder is active, the data output is A) A0 = 1 B) A0 = 0 C) A0 = 1 D) A0 = 0 A1 = 0 A1 = 1 A1 = 0 A1 = 1 A2 = 1 A2 = 0 A2 = 0 A2 = 1 24) 25) In VHDL combining the en bit with an 3-bit input to form a new 4-bit string is called A) concatenation. B) multiplexing. C) encoding. D) decoding. 25) 26) In order to select data input I3 of a 74151 eight-line multiplexer, the select inputs must be 26) A) E = 1 S0 = 1 S1 = 1 B) E = 0 S0 = 0 S1 = 0 C) E = 0 S0 = 1 S1 = 0 D) E = 0 S0 = 1 S1 = 1 S2 = 0 S2 = 1 S2 = 1 S2 = 0 27) Which input to a 7442 BCD-to-Decimal Decoder will cause all outputs to be HIGH? A) A3 -A0 = 0001 B) A3 -A0 = 1010 C) A3 -A0 = 0000 D) A3 -A0 = 1001 27) 28) In order to select data input I7 of a 74151 eight-line multiplexer, the select inputs must be 28) A) E = 0 S0 = 1 S1 = 1 B) E = 0 S0 = 1 S1 = 0 C) E = 0 S0 = 1 S1 = 1 D) E = 0 S0 = 0 S1 = 0 S2 = 0 S2 = 1 S2 = 1 S2 = 1 29) An octal-to-binary encoder has eight data inputs and encodes an output of ________ bits. A) two B) three C) four D) five 29) 30) When outputs b, c, f and g of a 7447 BCD-to-seven-segment code converter are active, what number will be shown on the display? A) 0 B) 3 C) 5 D) 4 30) 3 31) In order to select data input I6 of a 74151 eight-line multiplexer, the select inputs must be A) E=1 S0 =1 B) E=0 S0 =0 C) E=1 S0 =0 D) E=1 S0 =0 S2 =0 S2 =1 S2 =0 S2 =1 S1 =1 S1 =1 S1 =1 31) S1 =1 32) Output 5 of a 74138 octal decoder is selected when it is enabled by a data input of A) A0 = 1 B) A0 = 0 C) A0 = 1 D) A0 = 1 A1 = 0 A1 = 1 A1 = 0 A1 = 1 A2 = 0 A2 = 0 A2 = 1 A2 = 0 32) 33) A circuit that connects one of several inputs to its output is a A) decoder. B) comparator. C) multiplexer. D) counter. 33) 34) A device which places its input data onto one of several outputs is a A) demultiplexer. B) counter. C) multiplexer. D) comparator. 35) What is the binary value of the BCD number: 0011 0111 (37)? A) 0010 0111 B) 0110 0011 C) 0010 0101 D) 0011 0111 36) Which logic gate performs the comparator function? A) AND B) OR C) XNOR D) NAND 34) 35) 36) 37) When outputs a, b, c, d, e, and f of a 7447 BCD-to-seven-segment code converter are active, what number will be shown on the display? A) 0 B) 7 C) 6 D) 8 37) 38) A 74154 1-of-16 decoder has 16 outputs and decodes an input of ________ bits. A) two B) three C) four D) six 38) 39) A binary code which is used to indicate the position of a rotating shaft is the A) Gray code. B) BCD code. C) ASCII code. 39) D) octal code. 40) When outputs a, b, d, e, and g of a 7447 BCD-to-seven-segment code converter are active, what number will be shown on the display? A) 3 B) 2 C) 5 D) 4 40) 41) X's in the binary input columns of an IC indicate A) outputs. B) enabled. 41) C) don't care. D) disabled. 42) If the inputs of a 74139 dual four-line demultiplexer are as shown below, which output is correct? Ea = data A0a = 1 Eb = HIGH A0b = 0 A1a = 1 A1b = 1 A) 3a = data B) 3a = HIGH C) 2b = data 4 D) 1a = data 42) 43) When outputs a, b, c, d, and g of a 7447 BCD-to-seven-segment code converter are active, what number will be shown on the display? A) 0 B) 7 C) 5 D) 3 43) 44) How is the number zero (0) indicated on the outputs of a 7447 BCD-to-seven-segment code converter? A) Segments a, b, c, d, and e are active. B) Segments a, b, c, d, e, and f are active. C) All outputs are inactive. D) All segments are active. 44) 45) Which device is used in computer hardware to place ALU results into the correct register? A) demultiplexer B) encoder C) multiplexer D) decoder 45) 46) An everyday illustration of a multiplexer is A) the volume control in a stereo receiver. B) the balance control on a stereo receiver. C) the function switch on a stereo receiver. D) the treble-bass control on a stereo receiver. 46) 47) When data input I1 of a 74148 octal-to-binary encoder is active, the data output is A) A0 = 0 B) A0 = 0 C) A0 = 0 D) A0 = 1 A1 = 1 A1 = 0 A1 = 1 A1 = 0 A2 = 0 A2 = 1 A2 = 1 A2 = 0 47) 48) What input signals to the 74154 1 of 16 decoder will cause all outputs to be HIGH? 48) A) E0 or E1 are HIGH (disabled). B) A3 -A0 = 0000 C) E0 and E1 are LOW (enabled). D) A3 -A0 > 1001 49) Which input to a 7442 BCD-to-Decimal Decoder will cause output 3 to go LOW? A) A3 -A0 = 0110 B) A3 -A0 = 1100 C) A3 -A0 = 0111 D) A3 -A0 = 0011 49) 50) How is the number one (1) indicated on the outputs of a 7447 BCD-to-seven-segment code converter? A) Segment a is active. B) Segment b is active. C) Segments a and b are active. D) Segments b and c are active. 50) 51) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 1100 and B = 1100? A) A < B is 0 B) A < B is 0 C) A < B is 0 D) A < B is 1 A = B is 1 A > B is 0 A = B is 0 A = B is 0 A > B is 0 A > B is 1 A > B is 0 A > B is 0 51) 52) In VHDL, grouped inputs are called vectors, but a single output is a ________ quantity. A) phasor B) mono C) unique D) scalar 52) 53) What is the binary value of the BCD number: 1000 0001 (81)? A) 1000 0000 B) 0100 0001 C) 0110 0011 D) 0101 0001 53) 54) A multiplexer is also known as a(n) A) code converter. B) encoder. D) data selector. C) decoder. 5 54) 55) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 1001 and B = 1010? A) A < B is 1 B) A < B is 0 C) A < B is 0 D) A < B is 1 A = B is 0 A = B is 0 A = B is 1 A = B is 0 A > B is 0 A > B is 1 A > B is 0 A > B is 1 55) 56) What is the binary value of the BCD number: 0010 0111 0100 (274)? A) 0001 0001 0010 B) 1111 1110 C) 0001 0001 1110 56) D) 0001 0010 0010 57) Which device is used in computer hardware to interpret the binary code of the computer instruction? A) decoder B) multiplexer C) encoder D) demultiplexer 57) 58) How is the number five (5) indicated on the outputs of a 7447 BCD-to-seven-segment code converter? A) Segments a, c, d, f, and g active. B) Segments a, c, d, e, f, and g are active. C) Segments a, b, d, e, f, and g are active. D) Segments a, c, d, and g are active. 58) 59) A decimal-to-BCD encoder has ________ data inputs. A) two B) four C) five 59) D) ten 60) How is the number four (4) indicated on the outputs of a 7447 BCD-to-seven-segment code converter? A) Segments b, c, e, and g are active. B) Segments a, b, c, d, and g are active. C) Segments b, c, e, and f are active. D) Segments b, c, f, and g are active. 60) 61) Which device is used in computer hardware to select which register is to be gated to the ALU operand inputs? A) demultiplexer B) multiplexer C) encoder D) decoder 61) 62) Which data inputs to the 74154 1 of 16 Decoder will cause output 8 to be LOW? A) A3 -A0 = 1000 B) A3 -A0 = 0001 C) A3 -A0 = 0111 D) A3 -A0 = 1010 62) 63) Which device is used in the design of computer memory address selection hardware? A) encoder B) decoder C) demultiplexer D) multiplexer 63) 64) A device which generates a coded output from a singular active numeric input line is A) a multiplexer. B) a comparator. C) a decoder. D) an encoder. 64) 65) All outputs of the 74138 octal decoder are disabled (HIGH) when the enable inputs are ________. 65) A) E1 = 0, E2 = 1, and E3 = 1 B) E1 = 0, E2 = 0, and E3 = 0 C) E1 = 1, E2 = 1, and E3 = 0 D) all of the above 66) What are the outputs of a 7485 four-bit magnitude comparator when the inputs are A = 0011 and B = 0010? A) A < B is 0 B) A < B is 0 C) A < B is 1 D) A < B is 1 A = B is 1 A = B is 0 A = B is 0 A = B is 0 A > B is 0 A > B is 1 A > B is 1 A > B is 0 6 66) 67) The outputs of the 74138 octal decoder are enabled when the enable inputs are ________. A) E1 = 1, E2 = 1, and E3 = 0 B) E1 = 0, E2 = 0, and E3 = 0 C) E1 = 0, E2 = 0, and E3 = 1 D) E1 = 0, E2 = 1, and E3 = 1 68) The 74139 dual four-line demultiplexer functions as a demultiplexer if A) data input is on the A0 line. B) the E line is grounded. C) data input is on the E line. D) the A0 line is grounded. 67) 68) 69) Output 0 of a 74138 octal decoder is selected when it is enabled by a data input of A) A0 = 0 B) A0 = 1 C) A0 = 1 D) A0 = 0 A1 = 0 A1 = 0 A1 = 1 A1 = 1 A2 = 0 A2 = 0 A2 = 0 A2 = 1 69) 70) An eight-line multiplexer must have A) eight data inputs and two select inputs. C) eight data inputs and four select inputs. 70) B) four data inputs and three select inputs. D) eight data inputs and three select inputs. 71) A 1-of-8 octal decoder has eight outputs and decodes an input of ________ bits. A) four B) one C) three D) two 71) 72) Which device is used in computer hardware to select one of several inputs to be serviced by the computer program? A) decoder B) multiplexer C) demultiplexer D) encoder 72) 73) A four-line multiplexer must have A) four data inputs and two select inputs. C) four data inputs and four select inputs. 73) B) two data inputs and four select inputs. D) two data inputs and two select inputs. 74) The 74147 Decimal-to-BCD Encoder has LOW-active inputs and outputs. Which of the following is a true statement about this Encoder? A) The output when input 3 is LOW is A3-A0 = 1100. B) The output when input 7 is LOW is A3-A0 = 0111. C) The output when input 9 is HIGH is A3 -A0 = 0110. D) When no input is LOW, the outputs are all LOW. 74) 75) Output 3 of a 74138 octal decoder is selected when it is enabled by a data input of A) A0 = 1 B) A0 = 1 C) A0 = 0 D) A0 = 1 A1 = 0 A1 = 0 A1 = 1 A1 = 1 A2 = 0 A2 = 1 A2 = 1 A2 = 0 75) 76) The function of a magnitude comparator is to tell if A) A is greater than B. C) A is less than B. 76) B) A equals B. D) all of the above 7 77) If the inputs of a 74139 dual four-line demultiplexer are as shown below, which output is correct? Ea = LOW A0a = 0 77) Eb = HIGH A0b = 0 A1a = 1 A1b = 1 A) 3a = data B) 3a = HIGH C) 2a = LOW D) 2b = data 78) A demultiplexer is a device which A) selects one of several inputs to be placed onto one output line. B) generates an encoded output from a numeric input. C) routes a single data input onto one of several data outputs. D) converts some code into a recognizable number or character. 78) 79) The normal outputs of a magnitude comparator are A) A = B, A + B, and carry. C) Cin, Cout, and Sum. 79) B) Sum, difference, and carry. D) A < B, A = B, and A > B. 80) What is the binary value of the BCD number: 0001 1000 (18)? A) 0001 0010 B) 1000 0001 C) 1000 1000 D) 0001 1000 81) The 74139 dual four-line demultiplexer functions as a decoder if 81) A) data input is on the A0 line. B) the E line is grounded. C) data input is on the E line. D) the A0 line is grounded. 82) Which data inputs to the 74154 1 of 16 Decoder causes output 13 to be LOW? A) A3 -A0 = 1101 B) A3 -A0 = 1111 C) A3 -A0 = 1100 80) D) A3 -A0 = 1011 82) 83) The feature of Gray Code that makes it uniquely suited to control of rotating machinery is that A) each bit changes on every step of its count sequence. B) it can only have four bits. C) only one bit changes on each step of its count sequence. D) it is really an analog code. 83) 84) In order to select data input I5 of a 74151 eight-line multiplexer, the select inputs must be 84) A) E = 0 S0 = 0 S1 = 0 B) E = 1 S0 = 1 S1 = 1 C) E = 0 S0 = 1 S1 = 1 D) E = 0 S0 = 1 S1 = 0 S2 = 1 S2 = 0 S2 = 0 S2 = 1 8 Answer Key Testname: CHAP08Q 1) 2) 3) 4) 5) 6) 7) 8) 9) 10) 11) 12) 13) 14) 15) 16) 17) 18) 19) 20) 21) 22) 23) 24) 25) 26) 27) 28) 29) 30) 31) 32) 33) 34) 35) 36) 37) 38) 39) 40) 41) 42) 43) 44) 45) 46) 47) 48) 49) 50) A B C C A A D D C C A A C A D B C D D D B C D B A D B C B D B C C A C C A C A B C A D B A C C A D D 9 Answer Key Testname: CHAP08Q 51) 52) 53) 54) 55) 56) 57) 58) 59) 60) 61) 62) 63) 64) 65) 66) 67) 68) 69) 70) 71) 72) 73) 74) 75) 76) 77) 78) 79) 80) 81) 82) 83) 84) A D D D A A A B D D B A B D D B C C A D C D A A D D C C D A B A C D 10

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