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Clocked Logic:How counters work... (LESSON 3)

The JK Flip-Flop
(A simple improvement on the T Flip-Flop)

    By adding 3-input NAND gates to the master clocked RS Flip-Flop on a T Flip-Flop we can build a simple level clocked JK Flip-Flop.

T Flip-Flop
    Above: The original T Flip-Flop...

    Below: A modified T Flip-Flop, now called a JK Flip Flop...

JK Flip-Flop

    The only difference between these two flip flops is that the JK Flip-Flop has extra control inputs which allow it to have more versatility than its predesessor. For normal operation, (the toggle operation), J and K inputs are set high and remain high, just keep them connected to a positive (HIGH) power source.  In this mode, the JK Flip-Flop operates identical to the T Flip-Flop. If both J and K inputs are low, the Q outputs remain unchange, even when the clock input changes, it locks the output. Being able to freeze the ouput is a useful feature when constructing counters such as a stop watch! If K is held high while J is low, Q will go high on the next low level of the clock, after this point additional changes to the clock result in no change at the outputs. IF J is held high while K is held low, the reverse happens, and compliment of Q goes high on the next low level of the clock. So, in summary,  J and K can allow normal operation, disallow operation altogther, set Q or reset Q.


Clocked Logic: Lesson 2
Clocked Logic: Lesson 3
  Clocked Logic: Lesson 4