has two trip points and positive feedback

Why is the Schmitt trigger needed in the 60-Hz TTL-level clock pulse generator?

to provide a rounded pulse waveform

to provide a sharp pulse waveform

The main concern when using a pull-down resistor is:

the low power dissipation of the resistor

it will keep a floating terminal LOW

the high power dissipation of the resistor

Setup time specifies:

the maximum time interval required for the control levels to remain on the inputs before the triggered edge of the clock in order for the data to be reliably clocked out of the flip-flop

the minimum time the control levels need to be maintained on the inputs prior to the triggering edge of the clock in order to be reliably clocked into the flip-flop

the maximum time interval required for the control levels to remain on the inputs before the triggered edge of the clock in order for the data to be reliably clocked out of the flip-flop

how long the operator has to get the flip-flop running before the maximum power level is exceeded

how long it takes the output to change states after the clock has transitioned

Select the statement that best describes the parity method of error detection:

Parity checking is capable of detecting and correcting errors in transmitted codes.

Parity checking is best suited for detecting double-bit errors that occur during the transmission of codes from one location to another.

Parity checking is not suitable for detecting single-bit errors in transmitted codes.

Parity checking is best suited for detecting single-bit errors in transmitted codes.

Parity checking is capable of detecting and correcting errors in transmitted codes.

One disadvantage of the tracking A/D converter is:

the need for an accurate clock reference for the counter.

that it requires two counters one for up and one for down.

that the binary output will oscillate between two binary states when the analog input is constant.

the need for an accurate clock reference for the counter.

the need for a latch and its associated control circuit.

The quantization error in an analog-to-digital converter can be reduced by:

decreasing the number of bits in the counter and increasing the number of bits in the DAC.

increasing the number of bits in the counter and DAC.

decreasing the number of bits in the counter and increasing the number of bits in the DAC.

increasing the number of bits in the counter and decreasing the number of bits in the DAC.

decreasing the number of bits in the counter and DAC.

What is the function of the comparators in the 555 timer circuit?

to compare the output voltages to the external voltage divider

to compare the output voltages to the internal voltage divider

to compare the input voltages to the internal voltage divider

to compare the output voltages to the external voltage divider

to compare the input voltages to the external voltage divider

What does the discharge transistor do in the 555 timer circuit?

charge the external capacitor to stop the timing

charge the external capacitor to start the timing over again

discharge the external capacitor to stop the timing

discharge the external capacitor to start the timing over again

Why would a delay gate be needed for a digital circuit?

to provide for setup times and hold times

Which statement below best describes the function of a decoder?

Decoders are used to prevent improper operation of digital systems.

A decoder will convert a decimal number into the proper binary equivalent.

A decoder will convert a binary number into a specific output representing a particular character or digit.

Decoders are used to prevent improper operation of digital systems.

Decoders are special ICs that are used to make it possible for one brand of computer to talk to another.

A transducer is a device that:

converts analog data to meaningful data

converts a physical variable to an electrical variable

converts analog data to meaningful data

stores digital data and then processes that data according to a set of specified instructions

Refer to the keyboard encoder in figure (a). Sometimes when the 5 key is pressed, the system attached to the keypad does not respond. The 5 input on the 74147 is monitored with a digital storage scope while repeatedly pressing the 5 key, and the waveform in figure (b) is obtained; the P above the trace indicates the points at which the technician pressed the key. What is most likely wrong with the circuit?

The pull-up resistor connected to the 5 key is bad and should be replaced.

The switches on the 5 key are intermittent; the contacts need to be cleaned or the switch replaced.

The pull-up resistor connected to the 5 key is bad and should be replaced.

The common ground connection at the bottom of the 0 key has a bad solder connection; repair the connection.

The 74147 is intermittent, possibly due to high temperature, and should be replaced.

Which of the following describes the basic operation of a single-slope A/D converter.

A ramp voltage and analog input voltage are applied to a comparator. As the input voltage causes the integrating capacitor to charge, it will at some point equal the ramp voltage. The ramp voltage is measured and displayed on the digital panel meter.

The input voltage is used to set the frequency of a voltage-controlled oscillator (VCO). The VCO quits changing frequency when the input voltage stabilizes. The frequency of the VCO, which is proportional to the analog input voltage, is measured and is displayed on the digital display as a voltage reading.

A ramp generator is used to enable a counter through a comparator. When the ramp voltage equals the input voltage the counter is latched and then reset. The counter reading is proportional to the input voltage since the ramp is changing at a constant V/second rate.

A ramp voltage and analog input voltage are applied to a comparator. As the input voltage causes the integrating capacitor to charge, it will at some point equal the ramp voltage. The ramp voltage is measured and displayed on the digital panel meter.

Any of the above could be correct, depending on the specific type of A/D converter involved.

Which of the following is NOT a characteristic of a retriggerable monostable multivibrator?

It has no internal timing resistor.

It has an active-HIGH reset, which terminates all timing functions.

It has no internal timing resistor.

What is the difference between the 8031 and the 8051?

The 8051 has 64 bytes more memory.

2291 + Mcqs in Digital Electronics in Engineering Page 11 McqOptions

501.	A crystal demonstrates the ________ effect when a mechanical force across the crystal causes a small voltage to be generated.
A.	photoelectric
B.	Co-pitts
C.	piezoelectric
D.	flywheel
Answer» D. flywheel

502.	Can the automatic RC circuit be used to set a flip-flop rather than reset the flip-flop?
A.	yes
B.	no
Answer» B. no

503.	A Schmitt trigger:
A.	has two trip points
B.	is a zero crossing detector
C.	has positive feedback
D.	has two trip points and positive feedback
Answer» E.

504.	Why is the Schmitt trigger needed in the 60-Hz TTL-level clock pulse generator?
A.	to provide a triangle wave
B.	to provide a sine wave
C.	to provide a rounded pulse waveform
D.	to provide a sharp pulse waveform
Answer» E.

505.	The main concern when using a pull-down resistor is:
A.	the low power dissipation of the resistor
B.	it will keep a floating terminal LOW
C.	the high power dissipation of the resistor
D.	it will cause false triggering
Answer» D. it will cause false triggering

506.	What would be the output voltage of a 7814 voltage regulator?
A.	14 V dc
B.	+14 V dc
C.	8 V dc
D.	+8 V dc
Answer» C. 8 V dc

507.	Setup time specifies:
A.	the minimum time the control levels need to be maintained on the inputs prior to the triggering edge of the clock in order to be reliably clocked into the flip-flop
B.	the maximum time interval required for the control levels to remain on the inputs before the triggered edge of the clock in order for the data to be reliably clocked out of the flip-flop
C.	how long the operator has to get the flip-flop running before the maximum power level is exceeded
D.	how long it takes the output to change states after the clock has transitioned
Answer» B. the maximum time interval required for the control levels to remain on the inputs before the triggered edge of the clock in order for the data to be reliably clocked out of the flip-flop

508.	Select the statement that best describes the parity method of error detection:
A.	Parity checking is best suited for detecting double-bit errors that occur during the transmission of codes from one location to another.
B.	Parity checking is not suitable for detecting single-bit errors in transmitted codes.
C.	Parity checking is best suited for detecting single-bit errors in transmitted codes.
D.	Parity checking is capable of detecting and correcting errors in transmitted codes.
Answer» D. Parity checking is capable of detecting and correcting errors in transmitted codes.

509.	A logic circuit that provides a HIGH output for both inputs HIGH or both inputs LOW is a(n):
A.	Ex-NOR gate
B.	OR gate
C.	Ex-OR gate
D.	NAND gate
Answer» B. OR gate

510.	A 0.01-F capacitor is recommended by TTL manufacturers for ________ the power supply.
A.	decoupling
B.	filtering
C.	rectifying
D.	grounding
Answer» B. filtering

511.	Why does the data sheet for the 7476 only give a minimum value for the clock pulse width (both HIGH and LOW)?
A.	nominal value
B.	best-case condition
C.	worst-case condition
Answer» D.

513.	How is odd parity generated differently from even parity?
A.	The first output is inverted.
B.	The last output is inverted.
Answer» C.

516.	If the range of output voltage of a 6-bit DAC is 0 to 15 volts, what is the step voltage of the output?
A.	0.117 volt/step
B.	0.234 volt/step
C.	2.13 volts/step
D.	4.26 volts/step
Answer» C. 2.13 volts/step

517.	The main advantage of the successive-approximation A/D converter over the counter-ramp A/D converter is its:
A.	more complex circuitry
B.	less complex circuitry
C.	longer conversion time
D.	shorter conversion time
Answer» E.

518.	What is the current in the feedback resistor for the circuit given below?
A.	0.625 mA
B.	1.25 mA
C.	1.875 mA
D.	1.625 mA
Answer» D. 1.625 mA

512.	Identify the type of gate below from the equation
A.	Ex-NOR gate
B.	OR gate
C.	Ex-OR gate
D.	NAND gate
Answer» D. NAND gate

514.	One disadvantage of the tracking A/D converter is:
A.	that it requires two counters one for up and one for down.
B.	that the binary output will oscillate between two binary states when the analog input is constant.
C.	the need for an accurate clock reference for the counter.
D.	the need for a latch and its associated control circuit.
Answer» C. the need for an accurate clock reference for the counter.

515.	The quantization error in an analog-to-digital converter can be reduced by:
A.	increasing the number of bits in the counter and DAC.
B.	decreasing the number of bits in the counter and increasing the number of bits in the DAC.
C.	increasing the number of bits in the counter and decreasing the number of bits in the DAC.
D.	decreasing the number of bits in the counter and DAC.
Answer» B. decreasing the number of bits in the counter and increasing the number of bits in the DAC.

519.	The ________ is defined as the time the output is active divided by the total period of the output signal.
A.	on time
B.	off time
C.	duty cycle
D.	active ratio
Answer» D. active ratio

520.	Convert the following binary number to decimal. 01011₂
A.	11
B.	35
C.	15
D.	10
Answer» B. 35

521.	What is the function of the comparators in the 555 timer circuit?
A.	to compare the output voltages to the internal voltage divider
B.	to compare the input voltages to the internal voltage divider
C.	to compare the output voltages to the external voltage divider
D.	to compare the input voltages to the external voltage divider
Answer» C. to compare the output voltages to the external voltage divider

522.	A 22-k resistor and a 0.02-F capacitor are connected in series to a 5-V source. How long will it take the capacitor to charge to 3.4 V?
A.	0.44 ms
B.	0.501 ms
C.	0.66 ms
D.	0.70 ms
Answer» C. 0.66 ms

523.	What does the discharge transistor do in the 555 timer circuit?
A.	charge the external capacitor to stop the timing
B.	charge the external capacitor to start the timing over again
C.	discharge the external capacitor to stop the timing
D.	discharge the external capacitor to start the timing over again
Answer» E.

524.	The ________ circuit overcomes the problem of switching caused by jitter on the inputs.
A.	astable multivibrator
B.	monostable multivibrator
C.	bistable multivibrator
D.	Schmitt trigger
Answer» E.

525.	Why would a delay gate be needed for a digital circuit?
A.	A delay gate is never needed.
B.	to provide for setup times
C.	to provide for hold times
D.	to provide for setup times and hold times
Answer» E.

Explore topic-wise MCQs in Engineering.

A crystal demonstrates the ________ effect when a mechanical force across the crystal causes a small voltage to be generated.

Can the automatic RC circuit be used to set a flip-flop rather than reset the flip-flop?

A Schmitt trigger:

Why is the Schmitt trigger needed in the 60-Hz TTL-level clock pulse generator?

The main concern when using a pull-down resistor is:

What would be the output voltage of a 7814 voltage regulator?

Setup time specifies:

Select the statement that best describes the parity method of error detection:

A logic circuit that provides a HIGH output for both inputs HIGH or both inputs LOW is a(n):

A 0.01-F capacitor is recommended by TTL manufacturers for ________ the power supply.

Why does the data sheet for the 7476 only give a minimum value for the clock pulse width (both HIGH and LOW)?

Identify the type of gate below from the equation

How is odd parity generated differently from even parity?

One disadvantage of the tracking A/D converter is:

The quantization error in an analog-to-digital converter can be reduced by:

If the range of output voltage of a 6-bit DAC is 0 to 15 volts, what is the step voltage of the output?

The main advantage of the successive-approximation A/D converter over the counter-ramp A/D converter is its:

What is the current in the feedback resistor for the circuit given below?

The ________ is defined as the time the output is active divided by the total period of the output signal.

Convert the following binary number to decimal. 010112

What is the function of the comparators in the 555 timer circuit?

A 22-k resistor and a 0.02-F capacitor are connected in series to a 5-V source. How long will it take the capacitor to charge to 3.4 V?

What does the discharge transistor do in the 555 timer circuit?

The ________ circuit overcomes the problem of switching caused by jitter on the inputs.

Why would a delay gate be needed for a digital circuit?

A Schmitt trigger has VT+ = 2.0 V and VT = 1.2 V. What is the hysteresis voltage of the Schmitt trigger?

An optocoupler is an integrated circuit with an LED and a zener diode encased in the same package.

Which of the following circuit parameters would be most likely to limit the maximum operating frequency of a flip-flop?

Which statement below best describes the function of a decoder?

One can safely state that the output lines for a demultiplexer are under the direct control of the:

A transducer is a device that:

How many different voltages can be output from a DAC with a 6-bit resolution?

A 4-bit R/2R D/A converter has a reference of 5 V. What is the analog output for the input code 0101?

If an analog signal is to be converted to an 8-bit resolution, how many comparators are used in a parallel-encoded ADC?

Which of the following describes the basic operation of a single-slope A/D converter.

Decode the following ASCII message. 1010011101010010101011000100101100101000001001000100000110100101000100

Convert the binary number 1001.00102 to decimal.

The voltages in digital electronics are continuously variable.

A 0.3-F capacitor has an initial charge of 2.7 V. If it is discharged through a 10-k resistor for 6.5 ms, how much voltage will be left across the capacitor?

If the resistor in the Schmitt trigger astable multivibrator is a variable resistor, what part of the output voltage waveform will change when the resistance is changed?

Which of the following is NOT a characteristic of a retriggerable monostable multivibrator?

The pulse width out of a one-shot multivibrator increases when the:

What is the output pulse width of the waveform at the output of the circuit in the given figure?

What is another name for a bistable multivibrator?

An astable 555 timer has the following number of stable states:

Does the 74123 one shot have an internal timing resistor?

What is the difference between the 8031 and the 8051?

The I/O port that does not have a dual-purpose role is:

To interface external EPROM memory for applications, it is necessary to demultiplex the address/data lines of the 8051.

Convert the following binary number to decimal.
01011₂

A Schmitt trigger has V_T+ = 2.0 V and V_T = 1.2 V. What is the hysteresis voltage of the Schmitt trigger?

Decode the following ASCII message.

10100111010100101010110001001011001
01000001001000100000110100101000100

Convert the binary number 1001.0010₂ to decimal.

526.	A Schmitt trigger has V_T+ = 2.0 V and V_T = 1.2 V. What is the hysteresis voltage of the Schmitt trigger?
A.	0.4 volt
B.	0.6 volt
C.	0.8 volt
D.	1.2 volts
Answer» D. 1.2 volts

527.	An optocoupler is an integrated circuit with an LED and a zener diode encased in the same package.
A.	True
B.	False
Answer» C.

528.	Which of the following circuit parameters would be most likely to limit the maximum operating frequency of a flip-flop?
A.	setup and hold time
B.	clock pulse HIGH and LOW time
C.	propagation delay time
D.	clock transition time
Answer» D. clock transition time

529.	Which statement below best describes the function of a decoder?
A.	A decoder will convert a decimal number into the proper binary equivalent.
B.	A decoder will convert a binary number into a specific output representing a particular character or digit.
C.	Decoders are used to prevent improper operation of digital systems.
D.	Decoders are special ICs that are used to make it possible for one brand of computer to talk to another.
Answer» C. Decoders are used to prevent improper operation of digital systems.

530.	One can safely state that the output lines for a demultiplexer are under the direct control of the:
A.	input data select lines.
B.	the internal AND gates.
C.	the internal OR gate.
D.	Input data line.
Answer» B. the internal AND gates.

531.	A transducer is a device that:
A.	converts a physical variable to an electrical variable
B.	converts analog data to meaningful data
C.	controls a physical variable
D.	stores digital data and then processes that data according to a set of specified instructions
Answer» B. converts analog data to meaningful data

532.	How many different voltages can be output from a DAC with a 6-bit resolution?
A.	6
B.	16
C.	32
D.	64
Answer» E.

533.	A 4-bit R/2R D/A converter has a reference of 5 V. What is the analog output for the input code 0101?
A.	3.125 V
B.	0.3125 V
C.	0.78125 V
D.	3.125 V
Answer» E.

534.	Refer to the keyboard encoder in figure (a). Sometimes when the 5 key is pressed, the system attached to the keypad does not respond. The 5 input on the 74147 is monitored with a digital storage scope while repeatedly pressing the 5 key, and the waveform in figure (b) is obtained; the P above the trace indicates the points at which the technician pressed the key. What is most likely wrong with the circuit?
A.	The switches on the 5 key are intermittent; the contacts need to be cleaned or the switch replaced.
B.	The pull-up resistor connected to the 5 key is bad and should be replaced.
C.	The common ground connection at the bottom of the 0 key has a bad solder connection; repair the connection.
D.	The 74147 is intermittent, possibly due to high temperature, and should be replaced.
Answer» B. The pull-up resistor connected to the 5 key is bad and should be replaced.

535.	If an analog signal is to be converted to an 8-bit resolution, how many comparators are used in a parallel-encoded ADC?
A.	127
B.	128
C.	255
D.	256
Answer» E.