The JKFF simplifies the RSFF truth table but keeps two inputs (figure 7.22). The toggle state is useful in counting circuits. If the C pulse is too long this state is undefined and hence the JKFF can only be used with rigidly defined short clock pulses.
Figure 7.22: The basic JK flip-flop constructed from an
RS flip-flop and gates, and its schematic symbol and truth table.