Tutorial of 7473, Master - Slave J-K Flip - Flops with Complementary Outputs

          7473 is a commonly used Master-Slave J-K Flip-Flop IC. These ICs have two independant  Master-slave Flip-Flops with two complementary outputs. During the positive transistion of clock, data from J and K input is transferred to master and during the negative transistion of clock, data from master get transferred to the slave. If the clock is HIGH, no change will happen to the output ( Q and Qbar ), even if the value of J and K change. Output will change only during the negative transitions of clock. A logical LOW at CLR button will reset the outputs ( Q and Qbar ) and the outputs ( Q and Qbar ) will not change even if the J, K or CLK is changed. CLR should be set to HIGH after clearing the outputs.

          Circuit diagram to put one master-slave flip-flop in circuit is given below. Input pins ( J, K, CLK and CLR ) of the flip-flop is connected to 5V through pull up resistors. Push button switches are connected in between the inputs ( J, K, CLK and CLR ) and ground. These switches helps to shift the inputs between HIGH and LOW voltages. When the switch is OFF, corresponding input will be HIGH. Similarly, if the switch is ON, corresponding input will be LOW. 5V is given from a 5V Voltage regulator. Output is connected to LEDs through current limiting resistors.

Pinout diagram of 7473

          Pinout diagram of 7473 is given below. Each 7473 has two master-slave J K flip-flips. Half portion of IC, above VCC and ground constitutes the first flip-flop and the half portion below VCC and Ground constitutes the second master-slave flip-flop.

Truth Table of 7473

From the truth table, we can conclude that:

1. When CLR is LOW, Q will be LOW and Qbar will be HIGH. These outputs will not change, even if the other inputs ( J, K and CLK)  change, until CLR is set to HIGH.
2. When CLR becomes HIGH, if J is LOW and K is HIGH, Q becomes LOW and Qbar becomes HIGH during the next negative transition.
3. When CLR becomes HIGH, if J is HIGH and K is LOW, Q becomes HIGH and Qbar becomes LOW during the next negative transition.
4. When CLR becomes HIGH, if J and K are HIGH, Q and Qbar will toggle in each negative transitions.
5. When CLR becomes HIGH, if J and K are LOW, Q and Qbar will remain in the previous state and is independant of the state of CLK input.

Why pull up resistors ?.

          5V is given to J, K, CLK and CLR through pull up resistors. Pull up resistors helps to pull the inputs ( J, K, CLK and CLR )  to a HIGH value always. When any of the push button switch turns on, corresponding input ( J, K, CLK and CLR )  get grounded through the push button switch. That input ( J, K, CLK and CLR )  will get LOW voltage.

          If the same circuit is done without connecting the pull up resistors of proper resistance, when any of the swith turns on, power supply get shorted through the switch. High current will flow through the switch due to low resistance of the path. This may damage the power supply and gate operation will not take place.

Why push button switches ?.

          Push button switches are connected in between the inputs ( J, K, CLK and CLR ) and ground as shown in the circuit. Push button switch is most suitable for this purpose, because by default it will be in off state. A switch in off state means, corresponding input ( J, K, CLK and CLR ) gets a HIGH voltage. When a switch is pressed, that switch turns on and corresponding input ( J, K, CLK and CLR )  will get grounded and get a LOW voltage. When press is released switch will automatically turn off. 

Working 7473 can be pictorially represented as shown below.

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1. S1 - ON ,  CLR1 - LOW
    S2 - X    , K1 - X
    S3 - X    , J1 - X
    S4 - X    , CLK1 - X
    Q1 - LOW
    Q1bar - HIGH

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2. S1 - OFF   ,  CLR1 - HIGH
    S2 - ON     , K1 - LOW
    S3 - OFF    , J1 - HIGH
    S4 - OFF    , CLK1 - HIGH
    Q1 - LOW
    Q1bar - HIGH

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3. S1 - OFF   ,  CLR1 - HIGH
    S2 - ON     , K1 - LOW
    S3 - OFF    , J1 - HIGH
    S4 - ON      , CLK1 - LOW
    Q1 - HIGH
    Q1bar - LOW

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4. S1 - OFF   ,  CLR1 - HIGH
    S2 - ON     , K1 - LOW
    S3 - OFF    , J1 - HIGH
    S4 - OFF    , CLK1 - HIGH
    Q1 - HIGH
    Q1bar - LOW

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5. S1 - OFF   ,  CLR1 - HIGH
    S2 - OFF    , K1 - HIGH
    S3 - ON     , J1 - LOW
    S4 - OFF    , CLK1 - HIGH
    Q1 - HIGH
    Q1bar - LOW

6. S1 - OFF   ,  CLR1 - HIGH
    S2 - OFF    , K1 - HIGH
    S3 - ON     , J1 - LOW
    S4 - ON    , CLK1 - LOW
    Q1 - LOW
    Q1bar - HIGH

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 7. S1 - OFF   ,  CLR1 - HIGH
     S2 - OFF    , K1 - HIGH
     S3 - ON     , J1 - LOW
     S4 - OFF   , CLK1 - HIGH
     Q1 - LOW
     Q1bar - HIGH

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 8. S1 - OFF   , CLR1 - HIGH
     S2 - OFF   , K1 - HIGH
     S3 - OFF   , J1 - HIGH
     S4 - OFF   , CLK1 - HIGH
     Q1 - LOW
     Q1bar - HIGH

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 9. S1 - OFF   ,  CLR1 - HIGH
     S2 - OFF   , K1 - HIGH
     S3 - OFF   , J1 - HIGH
     S4 - ON    , CLK1 - LOW
     Q1 - HIGH
     Q1bar - LOW

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 10. S1 - OFF   ,  CLR1 - HIGH
       S2 - OFF   , K1 - HIGH
       S3 - OFF   , J1 - HIGH
       S4 - OFF   , CLK1 - HIGH
       Q1 - HIGH
       Q1bar - LOW

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 11. S1 - OFF   ,  CLR1 - HIGH
       S2 - OFF   , K1 - HIGH
       S3 - OFF   , J1 - HIGH
       S4 - ON    , CLK1 - LOW
       Q1 - LOW
       Q1bar - HIGH

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12. S1 - OFF   ,  CLR1 - HIGH
      S2 - OFF   , K1 - HIGH
      S3 - OFF   , J1 - HIGH
      S4 - OFF    , CLK1 - HIGH
      Q1 - LOW
      Q1bar - HIGH

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 13. S1 - OFF   ,  CLR1 - HIGH
       S2 - OFF   , K1 - HIGH
       S3 - OFF   , J1 - HIGH
       S4 - ON    , CLK1 - LOW
       Q1 - HIGH
       Q1bar - LOW

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14. S1 - OFF   ,  CLR1 - HIGH
      S2 - OFF   , K1 - HIGH
      S3 - OFF   , J1 - HIGH
      S4 - OFF   , CLK1 - HIGH
      Q1 - HIGH
      Q1bar - LOW

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15. S1 - OFF   ,  CLR1 - HIGH
      S2 - OFF   , K1 - HIGH
      S3 - OFF   , J1 - HIGH
      S4 - ON    , CLK1 - LOW
      Q1 - LOW
      Q1bar - HIGH

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16. S1 - OFF   ,  CLR1 - HIGH
      S2 - OFF   , K1 - HIGH
      S3 - OFF   , J1 - HIGH
      S4 - OFF   , CLK1 - HIGH
      Q1 - LOW
      Q1bar - HIGH

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17. S1 - OFF  ,  CLR1 - HIGH
      S2 - OFF   , K1 - HIGH
      S3 - OFF   , J1 - HIGH
      S4 - ON    , CLK1 - LOW
      Q1 - HIGH
      Q1bar - LOW

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