Test On Introduction to Digital Electronics

Test for Part One

Do not refer to the text when taking this test. You may draw diagrams or use a calculator if necessary. A good score is at least 38 correct answers. Answers are in the back of the book. It’s best to have a friend check your score the first time so you won’t memorize the answers if you want to take the test again.

1. The assertion ‘‘John is going to go out with the boys tonight or date Mary’’ is an example of:

(a) Negative logic

(b) The AND operation

(c) The inclusive OR operation

(d) The exclusive OR operation

2. Which symbol does not represent AND, OR or NOT?

(a) ‘‘*’’

(b) %

(c) ‘‘+’’

(d) ‘‘!’’

3. How would you create a three input NOR gate from two input NOR gates?

(a) Invert each input by passing them to a two input NOR gate and then combining it like the three input AND gate

(b) Pass two inputs to a NOR gate and pass this input to a second NOR gate along with the remaining input and invert the final result

(c) Pass two inputs to a NOR gate, use a second NOR gate to invert this NOR gate’s output and pass this result, along with the third input to a third NOR gate

(d) Pass two inputs to a NOR gate and pass this input to a second NOR gate along with the remaining input

4. ‘‘Product of sums’’ combinatorial logic circuits are not as common as ‘‘sum of products’’ because:

(a) They rely on ‘‘negative logic’’, which makes their operation more difficult to understand by simply looking at the circuit

(b) They are not as fast as product of sums combinatorial circuits

(c) Automated design tools are typically not programmed to work with product of sums circuits

(d) Product of sums combinatorial logic circuits cannot produce the same functions as sum of product combinatorial logic circuits

5. Which one of the following statements is false?

(a) Combinatorial logic circuits are drawn with inputs entering the gates from the left and exiting from the right

(b) Outputs from some of the gates in the combinatorial are passed

back so that they are part of their own inputs

(c) Combinatorial logic circuits can be designed to have true or

false outputs for given inputs

(d) The function of the individual gates in a combinatorial logic circuit does not change, even if the gates are used to provide a function which is radically different

6. Idealized waveform diagrams do not show:

(a) Potential ‘‘glitches’’ caused by gates changing state

(b) Delays in gates, responding to changes in inputs

(c) What happens with wiring problems such as when multiple outputs are connected to the same input

(d) All of the above

7. If an application has a critical speed requirement, you should design your circuit:

(a) To be as simple as possible, as this will minimize the delay a signal has passing through the circuit

(b) With as few gate delays as possible, while keeping an eye on the number of gates required as well as whether or not it can be efficiently implemented in the technology that you are using

(c) Using the fastest technology available

(d) Using computerized design systems

8. The NOR equivalent to an AND gate is:

(a) Built from two NOR gates and requires two gate delays for a signal to pass through

(b) Built from three NOR gates and requires three gate delays for a signal to pass through

(c) Built from three NOR gates and requires two gate delays for a signal to pass through

(d) Built from one NOR gate as well as a NOT gate and requires

two gate delays for a signal to pass through

9. When circling ‘‘1’’ outputs in a Karnaugh map:

(a) A maximum of two bits can only be circled at one time

(b) No bits can be circled more than once

(c) Each circle should be around a power of two number of bits

(d) Single bits on one side of a the map cannot be circled with bits on the other side

10. The four bit Karnaugh map

image

has the optimized sum of product equation:

(a) Output = (!B · !D) + (!A · !B) + (C · !D)+ (B · !C · D)

(b) Output= (A · B) + (!C · D) + (B · D) + (!B · C · !D)

(c) Output =(!C · !D) + (A · B)+ (B · D) + (!B · C · !D)

(d) Output = (A · B) + (!C · D) + (B · !D)+ (!B · C · !D)

11. Benjamin Franklin postulated:

(a) Electricity flows from positive to negative

(b) Lightning is dangerous

(c) Keys had to be charged before they would open doors

(d) Thomas Edison unfairly copied his work

12. The term ‘‘net’’ is used for:

(a) Wires in a circuit and lines on a circuit diagram

(b) Indicating the active signal lines of an ethernet cable

(c) A search tool through which information is passed through and relevant ‘‘hits’’ sticks to

(d) Nylon webbing used to protect a circuit against falling metal

components.

13. Knowing Ohm’s law and the resistance of a load and the voltage of a battery powering it, you can determine:

(a) The current passing through it

(b) The amount of water coming through an analogous pipe/tap/ hose

(c) Its equivalent parallel resistance

(d) The Thevenin equivalent circuit

14. Using the SI numbering methodology and symbols, 10,000,000 volts would be written out as:

(a) 10 million V

(b) 10 MV

(c) 10 mV

(d) 10,000,000 V

15. The voltage drop across a resistor in a series circuit:

(a) Cannot be calculated

(b) Is proportional to the power dissipated in the circuit

(c) Is always zero

(d) Is proportional to the resistor’s value relative to the total resistance in the circuit multiplied by the applied voltage

16. If a 10 ohm and 20 ohm resistor are in series, the equivalent resistance:

(a) Cannot be calculated without knowing the voltage applied

(b) 30 ohms

(c) 7.5 ohms

(d) 6.7 ohms

17. A 0.01 mF capacitor is most often used in:

(a) Radio applications; it has no use in digital electronics

(b) Decoupling digital electronic chips

(c) Filtering power supply ‘‘noise’’

(d) Ballast in fluorescent lighting

18. The value at a given time for the capacitor voltage in a resistor– capacitor low-pass filter circuit responding to a rising step input is:

(a) Infinite

(b) Defined by the formula V(t)= V – V x e-t/r

(c) Defined by the formula V(t) = V x e-t/r

(d) Zero; the capacitor has no voltage drop across it

19. The NOR gate was chosen as the basic CMOS logic gate because:

(a) It can be built most efficiently using MOSFET transistors

(b) It provides the fastest logic functions in CMOS logic

(c) It helps the circuit designer differentiate the functions provided by TTL and CMOS logic circuitry

(d) The NOR gate minimizes the power lost in the chip

20. Which statement is not a reason cited for using resistor pull ups and resistor/NOT gates for pull downs?

(a) The resistor can be connected to negative voltage without damaging the circuit

(b) Test equipment can easily change the state of logic pin inputs

(c) TTL and CMOS logic operate optimally with these circuits

(d) The resistor pull ups and resistor/NOT gate pull downs will work for both TTL and CMOS logic

21. If a silicon diode was passing 2 A of current, it would be dissipating:

(a) 14 watts of power

(b) 0.2 watts of power

(c) 0 watts of power

(d) 1.4 watts of power

22. In a 5 volt powered circuit, you have two LEDs in series and want to pass approximately 5 mA through them. What is the best current limiting resistor value should you use?

(a) 47 ohms

(b) 100 k ohms

(c) 5 ohms

(d) 1 k ohms

23. A bipolar transistor is best suited for:

(a) Radios and high-fidelity sound systems

(b) Small, high-density chips

(c) Memory circuits

(d) Low-power, high-density chips

24. The basic CMOS logic gate is:

(a) The NOT gate

(b) The AND gate

(c) The NOR gate

(d) The NAND gate

25. TTL is:

(a) Sound controlled

(b) Resistor controlled

(c) Current controlled

(d) Voltage controlled

26. When a TTL input is low:

(a) Current is being drawn from it

(b) A low voltage is being applied to it

(c) A ‘‘0’’ is being passed to it

(d) Electrons are being drawn from the emitter of the input gate’s NPN transistor

27. TTL/CMOS logic outputs:

(a) Can be used to drive neon lamps

(b) Can source/sink roughly 20 mA

(c) Cannot be used with different technology inputs

(d) Are limited to driving inputs less than 20 m away

28. ‘‘Fanout’’ is the term applied to:

(a) The number of outputs that can be driven by one input

(b) The number of fans required to cool a set number of chips

(c) The speed a signal travels through multiple paths of a logic chain

(d) The number of inputs that can be driven by one output

29. CMOS logic has the following characteristics:

(a) They are low speed, low power

(b) Require just about no power, regardless of the speed they operate at

(c) The current required is a function of the speed of operation

(d) Require less power than TTL because MOSFETs cannot be packed as tightly as bipolar transistors

30. LEDs are used in beginner digital electronic circuits:

(a) To indicate analog voltage levels

(b) To indicate a part is overheating

(c) To indicate input and output binary values

(d) To communicate with other circuits

31. The difference between 74Cxx and 74xx chips is:

(a) The 74Cxx is built from CMOS logic while the 74xx is TTL

(b) Signals in the 74Cxx propagate at the speed of light (as indicated by the ‘‘C’’ in the part number)

(c) The 74xx can work from 5 to 9 volts while the 74Cxx can only work with 5 volts

(d) The 74Cxx is built with a ‘‘compacted’’ chip

32. Gray codes were invented:

(a) To make your life miserable

(b) For simplifying Boolean logic statements

(c) For simplifying the task of determining the position of a device

(d) As a method of counting that was faster than binary

33. Adding 6 to 5 and getting the result 11 is the same as:

(a) Adding 7 to 4 and getting the result 11

(b) Adding 3 to 4 and getting the result 7 because in both cases, a prime number is produced

(c) Adding 5 to 6 using the commutative law and getting the result 11

(d) Adding 6 to 5, writing down ‘‘1’’ and then ‘‘10 x 1’’ because a carry digit is produced

34. The term ‘‘ripple’’ as applied to addition and subtraction is:

(a) The carry and borrow bits

(b) The result of the two single digit operation passed to the next significant digit

(c) The affect the operation has on its surrounding digits

(d) The oscillations caused by the need to carry and borrow data

35. Using the negated addition for subtraction, the borrow (negated carry) bit for the operation 5 – 6 is:

(a) Not required

(b) 1

(c) 0

(d) Indeterminate

36. A small circle on a gate’s input indicates:

(a) That the signal can only be used for output.

(b) That the signal is inverted before being passed to the gate

(c) Only open collector drivers can be used with this input

(d) The I/O can be used for monitoring the passage of the signal output in the gate

37. Magnitude comparators are based on:

(a) Three initial input state values

(b) Two four bit inputs

(c) Two subtracters

(d) One subtracter and one adder

38. Cascading chips is usually required because:

(a) Faster speed is required than a single chip can provide

(b) More bits must be processed than a single chip can handle

(c) The only chips that can provide all the necessary function require too much power

(d) It minimizes the cost of a circuit

39. Dividing a binary number by 8 can be accomplished by:

(a) Clearing the least significant three bits

(b) Shifting left three bits

(c) Shifting right three bits

(d) Setting the least significant three bits

40. Mickey Mouse logic solutions should be placed in the circuit:

(a) In the middle of a logic string

(b) On the inputs of a logic string

(c) On the outputs of a logic string

(d) Where high-current I/O is required

41. The resistor used in the Mickey Mouse logic AND gate shown in Fig. Test 1-1 should be:

(a) 10 k for TTL applications

(b) 10 k for CMOS applications

(c) The complementary one specified by the diode’s manufacturer

(d) Power rated for the load current of the application

image

42. Each item below is a disadvantage of a dotted AND bus except:

(a) High power consumption when the output is low

(b) The dotted AND bus has a slower response than tri-state buffers

(c) The dotted AND bus is cheaper than one manufactured with tri-state drivers

(d) It is very difficult to find open collector output chips

43. When providing multiple functions to a net, what logic technology/ technologies should be used?

(a) Just CMOS

(b) Just TTL

(c) CMOS receivers and TTL drivers

(d) TTL receivers and CMOS drivers

44. Sequential circuits contain:

(a) Memory devices

(b) Power supplies

(c) Input and output devices

(d) CMOS logic

45. Backdriving gates can:

(a) Simplify your application design

(b) Speed up gate operation

(c) Change the input of a downstream device

(d) Burn out the gate’s output transistors

46. What is the difference between ‘‘Q0’’ and ‘‘_Q0’’?

(a) There is no difference

(b) ‘‘Q0’’ is correct earlier than ‘‘_Q0’’

(c) ‘‘Q0’’ is current state of the flip flop and ‘‘_Q0’’ is the previous

(d) ‘‘_Q0’’ is the inverted value of ‘‘Q0’’

47. The ‘‘_Clr’’ pin of a D flip flop will:

(a) Set the bit

(b) Reset the bit

(c) Nothing

(d) Toggle the state of the bit

48. Which full D flip flop input pin is typically connected to the RC delay circuitry?

(a) D

(b) Clk

(c) _Clr

(d) _Pre

49. Which application is a register best suited for?

(a) Main memory in a computer system

(b) Permanently storing access passwords

(c) LED output states

(d) Temporary storage of data in a microprocessor

50. ‘‘Volatile memory’’ means:

(a) The contents of the memory device will not be lost when power is taken away

(b) The contents of the memory device will be lost when power is taken away

(c) The memory device is made up of a liquid which will evaporate if the chip package is broken

(d) Data is stored as patterns of a condensed gas

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