The basic NAND gate RS flip flop circuit is used to store the data and thus provides feedback from both of its outputs again back to its inputs. The RS flip flop actually has three inputs, SET, RESET and its current output Q relating to its current state.

 Truth Table for RS flip –flop

Clk

R

S

Q

Q^’

0

X

X

Previous or Memory State

1

1

0

0

1

1

0

1

1

0

1

0

0

Previous or Memory State

1

1

1

Invalid State