Category Archives: Academic

SR latches & flip-flop excitation tables

When studying for the exams of Digitale Elektronica II, I needed the excitation tables for a NAND SR latch. After constructing this myself, I wanted to verify on the internet if it was correct. On Wikipedia I’ve only found the excitation table for a NOR SR latch. When I’ve looked further, I found that many of the NAND SR excitation tables we’re mixed up with those of the NOR.

So I figured I would share the excitation tables here once and for all:

  • NOR SR latch
    Q(t) Q(t+1) S R
    0 0 0 x
    0 1 1 0
    1 0 0 1
    1 1 x 0
  • NAND SR latch
    Q(t) Q(t+1) S R
    0 0 1 x
    0 1 0 1
    1 0 1 0
    1 1 x 1

An “x” means “don’t care. You can easily make these yourself from the SR characteristic tables. As you can see, the values of SR are the complement for NOR and NAND (a 1 in the S or R column in the NAND table corresponds with a 0 in the same place in the NOR table and vice versa).