What is Setup and Hold time

by kamalnadh

 Setup:-

           It is the The minimum time required for the data to be stable before the clock edge.

Explanation:-

            Here we are considering two flip flops with same clock pulse.In above fig ff 1 sows the clock pulse of flip flop 1and ff 2 shows the clock pulse of flip flop 2.For setup we should consider data path.The data is launched at ff 1 and captured at ff 2.The data is launched at rising edge of ff 1 and it should be captured before the next rising edge of the ff 2 clock.If the data is captured before the next rising edge then the time is beneficial.If the data is captured after the next rising edge then violations will occur these are called setup violations.

                  In simple words the data should capture with in on full cycle.

                     

                   Setup slack = Required time – Arrival time 

Hold:-

                

          The minimum time required for the data to be stable after the clock edge.    

Explanation:-

                         

                            Here we are considering two flip flops with same clock pulse.In above fig ff 1 sows the clock pulse of flip flop 1and ff 2 shows the clock pulse of flip flop 2.For hold we are considering clock path.Here the data is launched and captured at the same edge.If the data is captured after the clock edge of the ff 2 then the time is benefited.If the data is captured before the clock edge of the ff 2 then violations will occur.These are called hold violations.

               In simple words the data should launch and capture at the same edge of the clocks.

                           Hold slack = Arrival time – Required time