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Flip Flops

Latches   are basic memory elements, Figure 42.


  
Figure 42: SR latch.
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Data can be set Q=1 by setting S=1, or cleared Q=0 by setting R=1, or stored by setting S=R=0. Latches are not clocked. Here is the truth table for the SR latch:

S R Q+ function
0 0 Q- store
0 1 0 reset
1 0 1 set
1 1 - -

Flip flops   are the basic memory element in a clocked circuits. They are essentially latches which are permitted to change state only at times determined by a clock signal,   Figure 43.


  
Figure 43: JK flip flop.
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Here is the truth table for the JK flip flop:

J K Q+ function
0 0 Q- store
0 1 0 reset
1 0 1 set
1 1 $\overline{Q}^-$ invert

A rising edge triggered JK flip flop is only permitted to change state at the time of the rising edge of the clock signal, Figure 44.


  
Figure 44: Rising edge triggered JK flip flop timing.
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