# Electrical Technology Grade 12 NSC November 2022 QP (Eng)

> Grade 12 Electrical Technology question paper from the NSC November Exam 2022 (English), 28 pages. Read online or download the free PDF.

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- Updated: 2026-09-27
- Subject: Electrical Technology
- Grade: Grade 12
- Document type: Question paper
- Year: 2022
- Exam period: NSC November Exam
- Curriculum: CAPS
- Pages: 28

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Electrical Technology · Grade 12 · NSC November Exam · 2022. Question paper, 28 pages. Read online or download the PDF.

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                                NATIONAL
                           SENIOR CERTIFICATE

                                   GRADE 12

             ELECTRICAL TECHNOLOGY: DIGITAL ELECTRONICS

                                NOVEMBER 2022

MARKS: 200

TIME: 3 hours

        This question paper consists of 18 pages, a 1-page formula sheet and
                              a 9-page answer sheet.

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Electrical Technology: Digital Electronics     2                            DBE/November 2022
                                              NSC

INSTRUCTIONS AND INFORMATION

1.         This question paper consists of SIX questions.

2.         Answer ALL the questions.

3.         Answer the following questions on the attached ANSWER SHEETS:

           QUESTIONS 3.2.4 and 3.3.4
           QUESTION 4.2.3
           QUESTIONS 5.2, 5.3.2, 5.4, 5.5.2, 5.7.1 and 5.8
           QUESTION 6.8

4.         Write your centre number and examination number on every ANSWER
           SHEET and hand them in with your ANSWER BOOK, whether you have used
           them or not.

5.         Sketches and diagrams must be large, neat and FULLY LABELLED.

6.         Show ALL calculations and round off answers correctly to TWO decimal
           places.

7.         Number the answers correctly according to the numbering system used in this
           question paper.

8.         You may use a non-programmable calculator.

9.         Calculations must include:

           9.1       Formulae and manipulations where needed

           9.2       Correct replacement of values

           9.3       Correct answer and relevant units where applicable

10.        A formula sheet is attached at the end of this question paper.

11.        Write neatly and legibly.

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Electrical Technology: Digital Electronics      3                              DBE/November 2022
                                               NSC

QUESTION 1: MULTIPLE-CHOICE QUESTIONS

Various options are provided as possible answers to the following questions. Choose
the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.15) in
the ANSWER BOOK, e.g. 1.16 D.

1.1        A/An … is an occurrence when a serious or unexpected dangerous situation
           occurs that requires immediate attention.

           A     evacuation procedure
           B     non-critical incident
           C     critical incident
           D     unsafe condition                                                                    (1)

1.2        A ... is used to eliminate switch bounce in electronics circuits.

           A     monostable multivibrator
           B     audio amplifier
           C     astable multivibrator
           D     oscillator                                                                          (1)

1.3        A circuit used in an audio mixer to individually amplify or attenuate each
           input signal is the ...

           A     comparator
           B     Schmitt trigger
           C     summing amplifier
           D     inverting op amp                                                                    (1)

1.4        A basic op-amp comparator circuit uses ...

           A     feedback.
           B     positive feedback.
           C     negative feedback.
           D     no feedback.                                                                        (1)

1.5        A ... produces an output which is directly proportional to the rate of change of
           the input signal

           A     passive RC integrator
           B     comparator
           C     passive RC differentiator
           D     non-inverting amplifier                                                             (1)

1.6        An op-amp circuit without any feedback has ... gain.

           A     closed-loop
           B     forward-loop
           C     reverse-loop
           D     open-loop                                                                           (1)

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Electrical Technology: Digital Electronics      4                            DBE/November 2022
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1.7        The pin that sets the voltage at which the 555 will trigger is known as ...

           A     output.
           B     discharge.
           C     threshold.
           D     reset.                                                                             (1)

1.8        A J-K flip-flop output is in a 'no change' condition when ...

           A     J = 1, K = 1.
           B     J = 1, K = 0.
           C     J = 0, K = 1.
           D     J = 0, K = 0.                                                                      (1)

1.9        Choose the correct number of flip-flops that are required to construct a
           decade counter:

           A     10
           B     8
           C     5
           D     4                                                                                  (1)

1.10       Counters that are not triggered at the same time are called ...

           A     asynchronous counters.
           B     modulus counters.
           C     propagation counters.
           D     synchronous counters.                                                              (1)

1.11       … is the type of register that would shift a complete binary number in one bit
           at a time and shift all the stored bits out one bit at a time.

           A     Parallel-in: parallel-out
           B     Series-in: series-out
           C     Parallel-in: series-out
           D     Series-in: parallel-out                                                            (1)

1.12       The term RAM means … with reference to microcontrollers.

           A     read all memory
           B     random allocation memory
           C     read and memorise memory
           D     random access memory                                                               (1)

1.13       The communication protocol that only requires two signal lines is called
           the ...

           A     Inter-integrated bus
           B     Serial communication interface
           C     Serial peripheral interface
           D     Serial dual interface                                                              (1)

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1.14       The RS-485 communication protocol has a maximum cable length of ...

           A     400 m.
           B     800 m.
           C     1 200 m.
           D     200 m.                                                                          (1)

1.15       A sequence of instructions that instructs a computer how to do a task is called
           a/an ...

           A     algorithm.
           B     program.
           C     flow chart.
           D     convention.                                                                     (1)
                                                                                                 [15]

QUESTION 2: OCCUPATIONAL HEALTH AND SAFETY

2.1        State TWO human rights in the workplace that ensure that the dignity of the
           employer is not infringed.                                                            (2)

2.2        State TWO evacuation steps to be followed when an emergency alarm is
           sounded in a workshop.                                                                (2)

2.3        Explain why the misuse of equipment in a workshop could cause a health or
           safety threat.                                                                        (2)

2.4        Refer to victimisation and state TWO actions by the employer that are
           forbidden.                                                                            (2)

2.5        State TWO types of risk analysis reports done by the health and safety
           representative.                                                                       (2)
                                                                                                 [10]

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Electrical Technology: Digital Electronics        6                                   DBE/November 2022
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QUESTION 3: SWITCHING CIRCUITS

3.1        State the difference between a monostable multivibrator and an astable
           multivibrator with reference to their output states.                                             (2)

3.2        FIGURE 3.2 shows a bistable multivibrator using a 555 IC. Answer the
           questions that follow.

                                         +6V

                 R2             R1
                10 kΩ          10 kΩ

                                                         8
                                                 4
                                                 7   555         3
                                                 6
                                                 2                                       LED
                                                     1       5
                     S1            S2
                                                                  C2               R3
                     Set        Reset
                                                                 10 nF            330 Ω

                   VCC                                                      Trigger input when
                                                                               S1 is pressed
                   0V
                   VCC                                                      Trigger input when
                                                                               S2 is pressed
                   0V
                   VCC
                                                                             Output
                   0V

                                FIGURE 3.2: BISTABLE MULTIVIBRATOR

           3.2.1       State ONE application of a bistable multivibrator.                                   (1)

           3.2.2       Explain why threshold pin 6 is connected directly to ground.                         (3)

           3.2.3       Explain what will happen to the input voltage on pin 2 if resistor R2 is
                       disconnected from the supply leaving it as an open circuit.                          (2)

           3.2.4       Draw the output         waveform          on   the   ANSWER      SHEET      for
                       QUESTION 3.2.4.                                                                      (3)

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3.3        FIGURE 3.3 shows a 741 monostable multivibrator circuit in its natural resting
           condition. Answer the questions that follow.

                                                             C1
                                                            1µF                                  +9 V
             VIN                                 VIN
             +9 V                                                                  VB                              VOUT
            VOUT                                                                                             C2
                                                                       R2                        -9 V
             -9 V
                                                                  -VREF                                      R3
             VB

                        FIGURE 3.3: 741 IC MONOSTABLE MULTIVIBRATOR

           3.3.1       State the purpose of C2 and R3.                                                                        (2)

           3.3.2       Determine the voltage at the non-inverting input (VB) when
                       capacitor C2 is fully charged to the saturation voltage of 9 V and no
                       current flows through R3.                                                                              (1)

           3.3.3       Explain what happens to the output voltage the moment a positive
                       input pulse is applied to the inverting input.                                                         (3)

           3.3.4       Draw the output                 waveform               on    the      ANSWER       SHEET      for
                       QUESTION 3.3.4.                                                                                        (4)

3.4        Refer to FIGURE 3.4 below and answer the questions that follow.

                                                                  RF

            VA
                                                                       +9 V                                         +9 V
                                                  VA                                      VOUT

           +VB                                         VB
                                                                                        R1                          -9 V
             0                                                         -9 V
                                             C
            -VB
                                     R2                                                 R2
                     VB = VOUT ×
                                   R1 + R2

                            FIGURE 3.4: 741 IC ASTABLE MULTIVIBRATOR

           3.4.1       Determine the polarity of VB when the output is positive.                                              (1)

           3.4.2       Refer to VA and VB and state when the output changes from
                       +9 V to –9 V.                                                                                          (1)
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           3.4.3       Describe how an increase in the value of RF affects the operation of
                       the circuit.                                                                     (3)

3.5        Refer to FIGURE 3.5 and answer the questions that follow.

                                                                     +9V
                                                 Input
             VIN                                                                          Output
                                                         VX
                                                                                    RF
                                                                     -9V

            +9 V
                                                                                    R1

            VOUT

             -9 V

                                      FIGURE 3.5: SCHMITT TRIGGER

           3.5.1       Determine the saturation voltages of the Schmitt trigger.                        (1)

           3.5.2       Explain the purpose of RF and R1 in the circuit.                                 (2)

           3.5.3       State when the output changes from high to low.                                  (2)

3.6        Explain the operation of the circuit in FIGURE 3.6.

                                                   +V
                +V
                                          Vref                 R1
              Input                                                         + Vcc
                  0                               Vin
                                      t
                                                                           741              VOUT
             + Vsat
            Output                                                          - Vcc
                                                              RREF
              - Vsat
                                      t

                                  FIGURE 3.6: OP-AMP COMPARATOR                                         (3)

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3.7        Refer to FIGURE 3.7 and answer the questions that follow.

                                                           RF 22 kΩ
                                       R1 22 kΩ

                                       R2 22 kΩ                 +12 V

                   V1                                       -

                          V2           R3 22 kΩ             +
                                                                                     VOUT
                                                                -12 V
                                 V3

                                        FIGURE 3.7: OP-AMP CIRCUIT

           Given:

           R1 = R2 = R3 = RF       =    22 kΩ
                          Vs       =    +12 V/-12 V
                          V1       =    0,9 V
                          V2       =    1,2 V
                          V3       =    2,1 V

           3.7.1        Identify the op-amp circuit in FIGURE 3.7.                                    (1)

           3.7.2        Determine the gain of the amplifier. Motivate your answer.                    (2)

           3.7.3        Calculate the output voltage.                                                 (3)

           3.7.4        Explain the effects of increasing the value of the feedback resistor.         (2)

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3.8        Refer to FIGURE 3.8 and answer the questions that follow.

                                                                      CF

                                                    RIN               +V
                                             VIN                  -
                   VIN
                                                                                        VOUT
                     0
                                                                  +
                                              t
                     0                                                -V
                VOUT

                   -V                                                                   0V

                                   FIGURE 3.8: OP-AMP INTEGRATOR

           3.8.1         State TWO factors that determine the output voltage of the circuit at
                         any time.                                                                    (2)

           3.8.2         Explain why capacitor CF charges at a fixed linear rate towards
                         –V when a positive square wave is fed to the input.                          (4)

           3.8.3         Explain the effect of a long RC time constant on the output.                 (2)
                                                                                                      [50]

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QUESTION 4: SEMICONDUCTOR DEVICES

4.1        Refer to FIGURE 4.1 and answer the questions that follow.

                                                         R F = 1, 4 kΩ

                                     RIN = 1 kΩ                      + 15 V
                                                     A       _

                                                             +                         VOUT
                                              0V                     - 15 V

                            FIGURE 4.1: INVERTING OPERATIONAL AMPLIFIER

           4.1.1       State the voltage at point A.                                                                   (1)

           4.1.2       Calculate the gain of the op amp.                                                               (3)

           4.1.3       State the phase relationship between the input and the output signal
                       when an AC signal is applied to the input.                                                      (1)

4.2        Refer to FIGURE 4.2 and answer the questions that follow.

                                                                                 VOUT / V

                                                                 D           A
                                                      +VSAT                             +13
                                                                                 +10
                                      RF
                                     39 kΩ                                       +5

                                                                         C       O
                      RIN                          VIN / V
                     3 kΩ                +V                   -2         -1                    +1         +2
                                     _                                            -5

           VIN
                                     +             VOUT                          -10
                            0V           -V                                      -13                           -VSAT
                                                                                                B          E

                                 A                                                             B

                            FIGURE 4.2: INVERTING OPERATIONAL AMPLIFIER

           4.2.1       Identify the saturation regions in FIGURE 4.2 B.                                                (2)

           4.2.2       Calculate the gain by using the voltage values on FIGURE 4.2 B.                                 (3)

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Electrical Technology: Digital Electronics         12                       DBE/November 2022
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           4.2.3      Draw the output waveform on the ANSWER                   SHEET      for
                      QUESTION 4.2.3 when the op amp is saturated.

                                             +V
                                             1
                                 Input                                 t
                                             -1
                                             -V
                                         +VSAT

                                 Output                                t

                                         -VSAT

                                                     FIGURE 4.2.3                                  (3)

           4.2.4      State TWO advantages of increasing the value of RF.                          (2)

4.3        Refer to FIGURE 4.3 and answer the questions that follow

                                0V       1                    8     +Vcc

                        TRIGGER          2                    7     DISCHARGE
                                                  555 IC
                         OUTPUT          3                    6     THRESHOLD

                           RESET         4                    5     CONTROL
                                                                    VOLTAGE

                                      FIGURE 4.3: 555 IC PIN LAYOUT

           4.3.1      State the function of pin 7.                                                 (1)

           4.3.2      Describe how the 555 IC is triggered with reference to pin 2.                (4)
                                                                                                   [20]

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Electrical Technology: Digital Electronics                   13                DBE/November 2022
                                                            NSC

QUESTION 5: DIGITAL AND SEQUENTIAL DEVICES

5.1        Refer to FIGURE 5.1 of a seven-segment display driver and answer the
           questions that follow.

                                                                       A

                                                                           b

                                                                           a
                                        16   3        12    10
                                                                           f
                                                                 6
                                                                           g
                        B           1             4026           7
                                                                           e
                                                                 11
                                        2    8   15   13     9
                                                                           d
                                                                           c

                                                                      0V

                            FIGURE 5.1: SEVEN-SEGMENT DISPLAY DRIVER

           5.1.1      Label blocks A and B.                                                          (2)

           5.1.2      Explain the main purpose of the seven-segment display driver.                  (2)

5.2        TABLE 5.2 shows the truth table of a two-digit binary-input to four-digit
           decimal-output decoder. Complete the equivalent logic circuit of this decoder
           on the ANSWER SHEET for QUESTION 5.2.

                            INPUTS                                  OUTPUTS
                        A               B                  0       1       2     3
                        0               0                  1       0       0     0
                        0               1                  0       1       0     0
                        1               0                  0       0       1     0
                        1               1                  0       0       0     1
                                                           TABLE 5.2                                 (5)

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5.3        Refer to FIGURE 5.3 of a half-adder and answer the questions that follow.

                                A

                                B                       X                Σ

                                                        Y                CO

                                         FIGURE 5.3: HALF-ADDER

           5.3.1      Name the gates represented by X and Y respectively.                           (2)

           5.3.2      Complete the truth table of the half-adder on the ANSWER SHEET
                      for QUESTION 5.3.2.

                                              A     B    Σ        Cout
                                              0     0    0         0
                                              0     1
                                              1     0
                                              1     1
                                                    TABLE 5.3.2                                     (6)

5.4        Refer to FIGURE 5.4 and complete the                     timing    diagrams     on
           ANSWER SHEET 5.4. Assume that Q starts LOW.

                                                        SET
                                                   J          Q
                                        CLK

                                                   K    CLR   Q
                                    FIGURE 5.4: CLOCKED J-K FLIP-FLOP                               (6)

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5.5        Refer to FIGURE 5.5 and answer the questions that follow.

            S
                                                   Q
                                                            S                             Q

                                                            R                             Q
                                                   Q
           R

                                                 FIGURE 5.5

           5.5.1      Identify the circuit in FIGURE 5.5.                                         (1)

           5.5.2      Complete the truth          table    on   the   ANSWER   SHEET     for
                      QUESTION 5.5.2.

                                              INPUTS            OUTPUTS
                                             S      R           Q     Q
                                             0          0
                                             0          1       1
                                             1          0
                                             1          1
                                                       TABLE 5.5.2                                (6)

5.6        Refer to counters and explain the following terms:

           5.6.1      Up counter                                                                  (2)

           5.6.2      Up/Down counter                                                             (2)

           5.6.3      Ripple counter                                                              (2)

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5.7        Refer to FIGURE 5.7 of a synchronous down counter and answer the
           questions that follow.

                      1                   A                       B                                   C

                            J         Q             J         Q                        J         Q

                            K     Q                 K     Q                            K     Q
                                FF0                     FF1                                FF2

            CLK

                           FIGURE 5.7: SYNCHRONOUS DOWN COUNTER

           5.7.1      Complete the timing diagrams for                this   counter       on        the
                      ANSWER SHEET for QUESTION 5.7.1.                                                     (8)

           5.7.2      Explain why the down counter operates faster than an up/down
                      counter.                                                                             (2)

5.8        Refer to shift registers as digital and sequential devices. Complete the sketch
           of a 4-bit PARALLEL-IN: SERIAL-OUT shift register using D-type flip-flops on
           the ANSWER SHEET for QUESTION 5.8 AND show ALL the inputs and
           outputs.                                                                                        (9)
                                                                                                           [55]

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QUESTION 6: MICROCONTROLLERS

6.1        Draw the block diagram of a microcontroller.                                                                                                       (5)

6.2        Refer to microcontrollers and explain how the control unit achieves its
           function.                                                                                                                                          (5)

6.3        Refer to the input/output pins of a microcontroller and answer the following
           questions:

           6.3.1      Explain the function of the TRIS (tristate) register.                                                                                   (2)

           6.3.2      Explain how the TRIS (tristate) register achieves its function.                                                                         (2)

6.4        Discuss the need for analogue-to-digital converters in microcontroller circuits.                                                                   (3)

6.5        Refer to FIGURE 6.5 and answer the questions that follow.

                                                                                                                 C
                                                    Acknowledge

            Data                A                                     Direction of data flow
                                                                                                                                    B            Data

                                           1 10011110 0               1 11010100 0                  1 01111010 0

                                                                      Stop bit          Start bit     Stop bit          Start bit
                                        Stop bit          Start bit
                                                   byte                          byte                            byte

                          FIGURE 6.5: ASYNCHRONOUS COMMUNICATION

           6.5.1      Label A, B and C.                                                                                                                       (3)

           6.5.2      Describe how data is transferred from A to B.                                                                                           (6)

           6.5.3      State TWO advantages of this method of communication.                                                                                   (2)

6.6        Refer to serial communication interface and answer the following questions:

           6.6.1      Write out the abbreviation SPI in full.                                                                                                 (1)

           6.6.2      State the mode of communication of the SPI.                                                                                             (1)

           6.6.3      Explain the operation of the SPI.                                                                                                       (4)

           6.6.4      State TWO advantages of the SPI.                                                                                                        (2)

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6.7        Refer to the software of microcontrollers and define the following terms:

           6.7.1      Looping                                                                    (2)

           6.7.2      Condition (IF statement)                                                   (3)

6.8        FIGURE 6.8 on the ANSWER SHEET shows an incomplete flow chart of a
           PICAXE car park assistance system with nine parking bays.

               This system will be set up at the entrance of the car park. It will consist of
                a red light and a green light.
               The green light informs the driver entering the car park that a parking
                space is available.
               The system will use two digital sensors.
               Sensor 1 will increase the count when cars enter the parking bay.
               Sensor 2 will decrease the count when cars exit the parking bay.
               Sensor 1 will increase the count to nine parking bays and the program will
                toggle to the red light.
               This will indicate a full car park.
               Sensor 2 will reduce the count. The green light switches on if the count is
                less than nine; therefore, indicating that a parking bay is available.

           Complete and label the flow chart of this device on the ANSWER SHEET for
           QUESTION 6.8.                                                                         (9)
                                                                                                 [50]

                                                                                     TOTAL:      200

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                                              FORMULA SHEET

SEMICONDUCTOR DEVICES

              VOUT       RF                            RF
Gain A V                          OR   A V  1
               VIN       R IN                          R IN
               R 
VOUT  VIN    F 
               R IN 
                 R 
VOUT  VIN  1  F 
                 RIN 
SWITCHING CIRCUITS

           R        R         R 
VOUT    V1 F  V2 F  ...VN F 
           R1       R2        RN 
               VOUT         VOUT
Gain A V           
                VIN   V1  V2  ...VN 
VOUT   (V1  V2  ...VN )

FLOW CHART SYMBOLS USED IN PICAXE

                              Process

                              Decision

                              Terminator

                                Data

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CENTRE NUMBER:

EXAMINATION NUMBER:

ANSWER SHEET

QUESTION 3: SWITCHING CIRCUITS

3.2.4
                 VCC
                                                            Trigger input when S1 is
                                                                    pressed
                 0V
                 VCC
                                                            Trigger input when S2 is
                                                                    pressed
                 0V
                 VCC
                                                              Output
                 0V

                                                                       Transfer mark to
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                                             FIGURE 3.2.4

                                                                                   MOD     (3)

3.3.4
                VIN

               +9 V

              VOUT

                -9 V

                 VB
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                                             FIGURE 3.3.4                          MOD     (4)

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4.2.3
                        +V
                         1
              Input                                  t
                         -1
                         -V
                      +VSAT

              Output                                 t

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                      -VSAT

                                             FIGURE 4.2.3
                                                                        MOD     (3)

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QUESTION 5: DIGITAL AND SEQUENTIAL DEVICES

5.2
               A

               B
                                                          0        Output 0

                                                          1        Output 1

                                                          2        Output 2

                                                          3        Output 3

                                             FIGURE 5.2
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                                                                           MOD    (5)

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5.3.2
                                             A   B         Σ   Cout

                                             0   0         0    0

                                             0   1

                                             1   0

                                             1   1

                                                 TABLE 5.3.2          Transfer mark to
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                                                                                  MOD     (6)

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5.4

                              1              2       3        4   5           6
            CLK

                  J

                  K

                  Q

                                                 FIGURE 5.4
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                                                                                   MOD    (6)

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5.5.2
                                              INPUTS      OUTPUTS
                                             S      R     Q     Q
                                             0     0
                                             0     1       1
                                             1     0
                                             1     1
                                                  TABLE 5.5.2
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                                                                                 MOD    (6)

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5.7.1

                           1          2      3         4      5   6   7            8
             CLK

                A

                B

                C

                                                 FIGURE 5.7

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                                                                                       MOD   (8)

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5.8

             High

             Clock

                       PD                    PC                PB        PA
                                                  FIGURE 5.8

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                                                                                  MOD    (9)

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QUESTION 6: MICROCONTROLLERS

6.8
                                               Start

                                             Green On
                                              Red Off

                                              Arrive?                Depart?
                                                         No                    No

                                             Yes                     Yes

                                                                                Transfer mark to
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                                                                                            MOD    (9)

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