The RS flip-flop (RSFF) is the result of cross-connecting two NOR gates as shown in figure 7.18. The RS inputs are referred to as active ones.
Figure 7.18: The RS flip-flop constructed from NOR gates,
and its circuit symbol and truth table.
The ideal flip-flop has only two rest states, set and reset, defined
by 
and 
, respectively.
A very similar flip-flop can be constructed using two NAND gates as
shown in figure 7.19.
The 
inputs are now active zeros.
Figure 7.19: The 
flip-flop constructed from
NAND gates, and its circuit symbol and truth table.
These FFs are often referred to as the set/reset type and are un-clocked.