Page 60 - CITS - Electronic Mechanic - TT - 2024
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ELECTRONICS MECHANIC - CITS




















           They are also known as twisted ring counters. The logic circuit given below shows a Johnson Counter. The circuit
           consists of four D flip-flops which are connected.

                                           Clock pulse    Q1       Q2     Q3     Q4

                                                0          0       0       0      1


                                                1          0       0       0      0

                                                2          1       0       0      0

                                                3          1       1       0      0

                                                4          1       1       1      0

                                                5          1       1       1      1

                                                6          0       1       1      1

                                                7          0       0       1      1

           Applications of Shift Registers
           •  The shift registers are used for temporary data storage.

           •  The shift registers are also used for data transfer and data manipulation.
           •  The serial-in serial-out and parallel-in parallel-out shift registers are used to produce time delay to digital circuits.
           •  The serial-in parallel-out shift register is used to convert serial data into parallel data thus they are used in
              communication lines where demultiplexing of a data line into several parallel lines is required.
           •  A Parallel in Serial out shift register is used to convert parallel data to serial data.
           An n-stage Johnson counter yields a count sequence of 2n different states, thus also known as a mod-2n counter.
           Since the circuit consists of four flip-flops the data pattern will repeat every eight clock pulses as shown in the truth
           table. The main advantage of the Johnson counter is that it only needs n number of flip-flops compared to the ring
           counter to circulate a given data to generate a sequence of 2n states.



















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                                    CITS : E & H - Electronics Mechanic - Lesson 9 - 29
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