Deck 9: MSI Logic Circuits

Question 1

The primary differences between a decoder and an encoder are:

A) decoders may have more than one input line active at any given time but only one output line will be active. Encoders also may have more than one input line active and may have more than one output line active at any given time.
B) decoders will have only one input line active but may have more than one output line active at any given time.
C) decoders may have only one input line and one output line active at any given time. Encoders may have more than one input and output lines active at any given time.
D) decoders may have more than one input line active but only one output line active at any given time. Encoders will have only one input active but may have more than one output line active at any given time.

Answer 1

decoders may have more than one input line active but only one output line active at any given time. Encoders will have only one input active but may have more than one output line active at any given time.

Question 2

Decoders may at first appear to be quite difficult to understand but they are really quite simple. You need only remember:

A) decoding is simply a procedure where each output line will be activated for only one of the possible combinations of inputs.
B) decoding is a complex operation that does not follow a set pattern. Consequently, the manufacturer's data sheet must be consulted for each possible input code group.
C) the inputs are always octal codes, therefore the output replicates the input.
D) decoding is totally random and completely accurate so the technician need not be concerned with how decoding is accomplished.

Answer 2

decoding is simply a procedure where each output line will be activated for only one of the possible combinations of inputs.

Question 3

A 16- input multiplexer is to be used to perform parallel- to- serial data conversion. Which of the following counters would be required to provide the data select inputs?

A) MOD- 8
B) MOD- 2
C) MOD- 4
D) MOD- 16

Answer 3

MOD- 16

Question 4

When cascading two 74HC85 magnitude comparators, the outputs of the______order comparator are the final outputs that indicate the results of the comparison.

A) high
B) low

Question 5

A multiplexer/data selector is a logic circuit that:

A) accepts data inputs from multiple lines and passes this data to multiple output lines.
B) accepts data inputs from several lines and multiplexes this input data to four BCD lines.
C) accepts data inputs from one line and passes this data to multiple output lines.
D) accepts data inputs from several lines and allows one of them at a time to pass to the output.

Question 6

A BCD to decimal decoder would be required to have:

A) three input lines and nine output lines.
B) four input lines and ten output lines.
C) nine input lines and three output lines.
D) ten input lines and four output lines.

Question 7

Decoders are normally used whenever:

A) an output or group of outputs is to be activated only when a specific combination of inputs occur.
B) inputs are totally random and the active outputs are nonsequential.
C) outputs are to be activated on a random time- share basis independent of the input combinations.
D) outputs are to be activated that are identical to the multiple inputs.

Question 8

A demultiplexer accepts data from:

A) multiple input lines and transfers it to one output line.
B) sequential input lines and transfers it to one output line.
C) one input line and transfers it to one output line after conditioning and buffering the data signals.
D) one input line and transfers it to multiple output lines.

Question 9

A three- line- to- eight line decoder has inputs CBA where A is the LSB. The output AND gates are labeled Q₀ through Q₇. The output of AND gate Q₄ should be active when the inputs are:

A)
B)
C)
D)

Question 10

The IEEE/ANSI symbol for a decoder has the internal designation BCD/DEC. This means the decoder is a:

A) binary coded decimal to decimal decoder with ten inputs and four outputs.
B) binary coded decimal to decimal decoder with four inputs and ten outputs.
C) decimal to binary coded decimal decoder with ten inputs and four outputs.
D) decimal to binary coded decimal decoder with four inputs and ten outputs.

Question 11

The IEEE/ANSI symbol for a decoder has the internal designation BCD/DEC, how many pins; including V_cc and ground, would this IC have?

A) 18
B) 14
C) 16
D) 20

Question 12

The parallel data from a branch bank's computer terminal is to be transferred over telephone lines to the main bank's computer. You would expect to find a______at the transmitting end and _____at the receiving end.

A) multiplexer, demultiplexer
B) demultiplexer, multiplexer

Question 13

CMOS devices are generally used to drive 7- segment LCD displays because:

A) they consume less power than TTL devices and their output in the LOW state is always above
0)5 v.
B) they are capable of generating an output ac sinewave to drive the 7- segment LCD.
C) they consume less power than TTL devices and their output voltage in the LOW state is usually less than TTL.
D) they consume more power than TTL devices but their output voltage in the LOW state is less than TTL and this extends the useful life of the LCD.

Question 14

One would normally expect a 16- input multiplexer to have a minimum of:

A) 16- input data lines and three input select lines.
B) 16- input data lines and five input select lines.
C) 16- input data lines and two input select lines.
D) 16- input data lines and four input select lines

Question 15

How many binary output lines would be required for a four- digit BCD- to- binary converter?

A) 10
B) 16
C) 12
D) 14

Question 16

A certain BCD- to- decimal decoder has four input lines and 10 output lines. If four input lines are capable of 16 possible combinations and only 10 output combinations are required, why have four inputs?

A) With three input lines the maximum number of output combinations would be equal to nine, including zero, and this would be sufficient, but decoders are not manufactured with only three inputs.
B) With four input lines, the decoder can provide for those rare occasions when input codes greater than 1001₂ may require decoding.
C) With three input lines the maximum number of output combinations would be limited to eight.
D) Both A and C

Question 17

A decoder has outputs labeled through https://d2lvgg3v3hfg70.cloudfront.net/TB9839/. The output gates for this device are:

A) NAND gates.
B) NOR gates.
C) AND gates.
D) XNOR gates.

Question 18

The decoder described in the preceding question has three inputs labeled A₂, A₁, and A₀ where A₂ is the MSB. If the input is 010₂, the conditions of the output gates should be:

A) output HIGH and all other gate outputs LOW.
B) 11eea485_0f90_d70c_97f4_83c4ed9fa336_TB9839_11output LOW and all other gate outputs HIGH.
C) output HIGH and all other gate outputs LOW.
D) 11eea485_1fa8_415d_97f4_05e2805d980c_TB9839_11output LOW and all other gate outputs HIGH

Question 19

Multiplexing of digital signals is usually required when:

A) moving data over long distance transmission lines.
B) moving data internally within a microprocessor.
C) moving data between memory and storage registers in a microprocessor.
D) Both A and C

Question 20

A 7445 decoder has IEEE/ANSI symbol internal markings of BCD/DEC with a small triangle underneath. Also, there is an underlined diamond at each output. These symbols mean the device is a:

A) BCD to decimal decoder buffer/driver with open- collector outputs.
B) BCD buffer/driver with totem- pole outputs.
C) decimal buffer/driver with open- collector outputs.
D) BCD to decimal decoder buffer/driver with totem- pole outputs.

Question 21

Bus contention arises when more than one register output is "enabled" at the same time on a single data bus line. This condition will cause:

A) uncertain logic levels and possible damage to the register output buffers.
B) uncertain logic levels and possible damage to the input data lines of the registers contending for the bus.
C) uncertain logic levels and possible damage to the bus line.

Question 22

Which of the following 7- segment displays would be best suited for operation in a totally dark environment?

A) 7- segment LED
B) 7- segment LCD
C) Either A or B

Question 23

How many input lines would be required for a 1- of- 8 decoder?

A) 5
B) 3
C) 2
D) 4

Question 24

The output lines for a demultiplexer are under the direct control of the:

A) input data- select lines.
B) internal AND gates.
C) internal OR gate.
D) input data line.

Question 25

The code conversion process for a two- digit BCD to binary converter would require _____ inputs and would have an output of _____binary bits.

A) Four two bit code group, seven
B) Four two bit code group, six
C) Two four bit code group, six
D) Two four bit code group, seven

Question 26

Select the statement which best describes the application of observation and analysis procedures when troubleshooting complex circuits.

A) A thorough understanding of the proper operation of the test equipment to be used to analyze the fault.
B) A thorough understanding of the operation of the circuit, observing the symptoms caused by the failure and using human reasoning to isolate the fault to a specific area.
C) The capabilities of modern test equipment have virtually eliminated the requirement for observation and analysis procedures when troubleshooting.

Question 27

In a 1- of- 10 BCD- to- decimal decoder:

A) only one output line is activated at any one time.
B) output lines 0- 9 will be activated with any valid input BCD code.
C) ten output lines are usually activated at the same time.
D) output line four will be activated when the input code is 0101₂.

Question 28

More than one active input to an encoder will often produce an erroneous output. This problem may be partially overcome by the use of:

A) an open- collector NAND gate whose inputs are connected to the decoder's outputs.
B) an additional encoder whose inputs are cascaded to the original decoder's outputs.
C) a priority encoder to ensure that when more than one input is active the output will correspond to the lowest- numbered input.
D) a priority encoder to ensure that when more than one input is active the output will correspond to the highest- numbered input.

Question 29

When different sets of data are appearing on the same output line at different times, the data is:

A) time- division multiplexed.
B) frequency- shifted multiplexed.
C) frequency- shifted demultiplexed.
D) time- division demultiplexed.

Question 30

A three line- to- eight line decoder could also be called a(n):

A) binary to octal decoder.
B) binary to hexadecimal decoder.
C) hexadecimal to binary decoder.
D) octal to binary decoder.

Question 31

Which of the following groups of terms best describes the inputs and the components associated with a multiplexer?

A) Input address lines, inverters, AND gates, and an output OR gate
B) Input data lines, inverters, AND gates, and an output OR gate
C) Input address lines, input data lines, inverters, AND gates, and an output OR gate
D) Input binary data lines, inverters, AND gates, and an output NAND gate

Question 32

What is the purpose of a decoder's enable inputs?

A) To disable the decoder outputs so that all outputs will be inactive
B) To disable the inputs and activate all outputs
C) To allow the decoder to respond to the inputs to activate the correct output gate
D) Both A and C

Question 33

Internal computer registers that store data are often connected to the computer data bus lines by:

A) totem- pole output devices.
B) quad input AND gates.
C) open- collector devices.
D) tri- state buffers.

Question 34

A BCD decoder that has active HIGH outputs would require a common_____7- segment LED display.

A) cathode
B) anode or common cathode
C) anode
D) Neither a common anode or a common cathode 7- segment LED would be satisfactory for this decoder.

Question 35

A 74HC85 magnitude comparator is used to:

A) compare two input voltage levels and generate outputs to indicate which voltage has the greater magnitude.
B) AND two binary quantities and generate outputs only if they are equal in magnitude.
C) Exclusive OR two binary quantities and generate an output if they are unequal in magnitude.
D) compare two input binary quantities and generate outputs to indicate which quantity has the greater magnitude.

Question 36

As compared to regular registers, bidirectional registers generally have:

A) a greater number of bus connections and separate I/O lines.
B) fewer bus corrections and separate I/O lines.
C) a greater number of bus connections and common I/O lines.
D) fewer bus connections and common I/O lines.

Question 37

A numeric display - driven by a 744X driver - is used to display the output from a BCD counter. If this counter only displays the numbers 0, 2, 4, 6, and 8, then troubleshooting should be narrowed down to:

A) the "b", "c", and "d" segments on the numeric display.
B) the MSB line on the display input circuit.
C) the MSB line on the driver input circuit.
D) the LSB line on the display input circuit.
E) the LSB line on the driver input circuit.

Question 38

The basic advantage of active- matrix displays over passive LCD displays is that active matrix displays have_____resolution and _____ response times.

A) higher, shorter
B) lower, longer
C) lower, shorter
D) higher, longer

Question 39

Two eight input multiplexers can combine to send data over a single output line. The first step is combining select inputs. To complete the circuit:

A) the enable inputs must be connected together.
B) connect one enable input to the other via and inverter, then connect outputs together through an OR gate.
C) a NOR gate must tie output lines together.
D) tie enables inputs together and install a NAND gate on the outputs.

Question 40

Magnitude comparators are useful for speed control, temperature control, and level control. After these analog quantities are sampled:

A) quantities are permanently stored in memory location.
B) quantities are converted to binary equivalent.
C) quantities are converted to a constant current source.
D) quantities are converted to equivalent frequency through another converter.

Question 41

An eight input multiplexer can easily be converted for use as a parallel to serial converter. What would be the appropriate way to sequence the data select inputs?

A) Use a MOD 8 Asynchronous converter.
B) Use three Asynchronous FF's as converters.
C) Use three synchronous FF's as converters.
D) Both A and C

Question 42

Approximately how much current would be required to operate the number 6 on a 7- segment LED display if each segment requires 10 mA?

A) 70 mA
B) 60 mA
C) 40 mA
D) 50 mA

Question 43

It is normal for more than one decoder output to be active at the same time.

Question 44

The select inputs to a multiplexer may also be called address lines.

Question 45

A demultiplexer does not use an OR gate as the output gate because of the multiple output lines.

Question 46

The relatively slow transition time of data on bus lines may be attributed directly to capacitive loading of the lines.

Question 47

Usually, a decoder circuit without bubbles on the outputs has only one output HIGH while all the other outputs are LOW.

Question 48

Incandescent 7- segment displays are especially well suited for use in portable battery- operated devices.

Question 49

Basically, a multiplexer changes parallel data inputs to a serial output.

Question 50

The circuit for a decoder is basically the same as for a multiplexer.

Question 51

Modern computers transfer data between different devices over a common set of connecting lines called a data bus.

Question 52

All decoder inputs correspond to a decoder decimal equivalent output.

Question 53

Decoder/drivers, like the TTL7445 can be used to drive loads such as LEDs, lamps, relays, and small DC motors.

Question 54

Common anode seven segment displays could be considered active high loads.

Question 55

In contrast to other types of decoders, display decoder/drivers activate more than one output for any given input.

Question 56

LCD displays are more visible in low light conditions than LED displays.

Question 57

LCD displays require less current than LEDs.

Question 58

Alphanumeric LCD displays interfaces are standardized so that an LCD module from any manufacturer uses the same signal and data format.

Question 59

Number system conversion can be accomplished using encoders.

Question 60

Storing three digits entered by a keypad would require two four- bit registers.

Question 61

A _____is a logic circuit that accepts a set of inputs which represents a binary number, and activates only the output that corresponds to that input number.

Question 62

Some decoders have one or more _____ inputs that are used to control the operation of the decoder.

Question 63

A(n)_____ display generates or emits light energy as current is passed through the individual segments.

Question 64

A(n) _____display controls the reflection of available light.

Question 65

Circuits in the _____logic family are generally used to drive LCDs.

Question 66

A(n) _____ has a number of input lines, only one of which is activated at a given time, and produces an N- bit output code, depending on which input is activated.

Question 67

A digital_____or data selector is a logic circuit that accepts several digital data inputs and selects one of them at any given time to pass on to the output.

Question 68

A _____takes thee data applied to a single input and distributes it over several outputs.

Question 69

A _____comparator is a combinational logic circuit that compares two input binary quantities and generates outputs to indicate which one has the greater magnitude.

Question 70

A code_____is a logic circuit that changes data presented in one type of binary code to another type of binary code.

Question 71

I/O lines that transfer data in either of two directions depending on the state of their enable inputs are called _____data lines.

Question 72

In order to decode a multiplexer from a remote location, a _____must share the same address or select bits.

Question 73

Magnitude comparators compare a measured quantity to a _____value.

Question 74

A four- bit magnitude comparator could be _____ with another four- bit comparator to increase resolution.

Question 75

To prevent bus contention problems from occurring from multiple input sources tied to a data bus, every source is connected through _____and held in Hi- Z state by output enable inputs.

Question 76

Data can be transferred to or taken from a data bus through tri- state_____, which accept and send data when enabled.

Question 77

Hi- Z or _____state buffers data bus from register, ADCs, DACs, and other devices.

Question 78

In the event that a 9 and a 1 were entered simultaneously, a _____encoder would encode only the 9.