Summary

• We have considered two simple example for sequential logic circuits.
• Common characteristics of sequential logic circuits are:
  • The use of memory elements and combinatorial logic gates.
  • The inputs to the flipflops depend on both external inputs and the current outputs of the flipflops.
• Consequently, the next state (outputs of the flipflops) depends on the current state.
• In the circuits we considered, the external inputs (buttons) were connected to the Enable inputs.
• Such circuits are often called asynchronous as they keep track of events that occur at arbitrary instants of time.
• Synchronous circuits in contrast operate on a periodic basis and the Enable input is connected to a common clock signal.
• Shift-register circuits are examples of synchronous sequential logic.