Digital Logic -Sequential Logic

Digital LogicDigital LogicDDigital Logic-Sequential Logic

Sequential circuits use current input variables and previous input variables by   storeing the information and putting back into the circuit on the next clock (activation) cycle.

  -Output determined by inputs

   and previous outputs(memory)

 -Feedback loop.

Flip-flop.

Flip-flop has the storage element where the stated this element is a function of the previous inputs to the circuit.

-store data on a rising or falling trigger edge

-Basis of important computer components:

 * memory

 * counter

(Set-Reset) SR Flip Flop Truth table.

-Values vary over time. 

- S(t), R(t), Q(t) denote value at time t.

timing diagram for SR flip-flop

Clock

- Fundamental abstraction.

*regular on-off pulse

-External analog device.

-Synchronizes operations of different circuit elements.

- 1 GHz clock means 1 billion pulses per second.

• Sequential circuits that are regulated by a clock

   signal are said to be synchronous.

  Basic Flip Flop

Registers

• A register is an array of flip-flops that is used to

store or manipulate the bits of a digital word.

Example: Serial-In, Parallel-Out Shift Register

Summary

• Logic gates can be interconnected to form flipflops.

• Interconnections of flip-flops form registers.

• A complex digital system such as a computer

consists of many gates, flip-flops, and registers. 

Thus, logic gates are the basic building blocks

for complex digital systems.

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