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