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Questions and Answers
What is the main difference between combinational circuits and sequential circuits?
What is the main difference between combinational circuits and sequential circuits?
What is the function of storage elements in sequential circuits?
What is the function of storage elements in sequential circuits?
What determines the outputs of a sequential circuit?
What determines the outputs of a sequential circuit?
What is the purpose of state tables and state diagrams in sequential circuit analysis?
What is the purpose of state tables and state diagrams in sequential circuit analysis?
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What is the primary function of a latch?
What is the primary function of a latch?
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What is the primary function of a storage element in a sequential circuit?
What is the primary function of a storage element in a sequential circuit?
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What is the main difference between synchronous and asynchronous sequential circuits?
What is the main difference between synchronous and asynchronous sequential circuits?
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What is the purpose of the clock signal in a synchronous sequential circuit?
What is the purpose of the clock signal in a synchronous sequential circuit?
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What is the problem with the basic SR latch when SR=11?
What is the problem with the basic SR latch when SR=11?
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What is the advantage of a D latch over a basic SR latch?
What is the advantage of a D latch over a basic SR latch?
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Study Notes
Sequential Circuits
- A sequential circuit has two main components: combinational logic and storage elements.
- Output function: Outputs = g(Inputs, State)
- Next state function: Next State = f(Inputs, State)
Types of Sequential Circuits
- Synchronous circuits:
- Behavior defined from knowledge of signals at discrete instances of time
- Storage elements observe inputs and change state only in relation to a timing signal (clock pulses)
- Asynchronous circuits:
- Behavior defined from knowledge of inputs at any instant of time and the order in which inputs change
- If clock is regarded as another input, all circuits are asynchronous
Storage Elements: Latches
- Latches are asynchronous storage circuits
- The major difference among storage elements is in the number of inputs they possess and how they affect the binary state
- Types of latches:
- SR Latches
- D Latches
SR Latch
- Cross-coupling two NOR gates gives the S-R Latch
- Function diagram: Q = (R+Q')', Q' = (S+Q)'
- Truth table:
- Q(t+1) = Q(t) if R=0 and S=0
- Q(t+1) = 0 if R=1 and S=0
- Q(t+1) = 1 if R=0 and S=1
- Q(t+1) = undefined if R=1 and S=1
Problems with SR Latch
- If SR=11, both Qnext and Q'next would become 0, which contradicts the assumption that Q and Q' are always complemented
- If S=0 and R=0, the circuit enters an infinite loop where Q and Q' cycle between 0 and 1 forever
Clocked SR Latch
- Adding two NAND gates to the basic S-R latch gives the clocked S-R latch
- Has a time sequence behavior similar to the basic S-R latch except that the S and R inputs are only observed when the clock line C is high
D Latch (Transparent Latch)
- Adding an inverter to the S-R latch gives the D latch
- Note that there are no "indeterminate" states (solves the S-R latch problem)
Overview of Sequential Circuits
- Storage elements: Latches or Flip-Flops
- Introduction to sequential circuits
- Types of sequential circuits
- Storage elements: Latches, Flip-Flops
- Sequential circuit analysis: State tables, State diagrams
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Description
Review of synchronous sequential circuits, including logic circuits, combinational circuits, and storage elements. Learn about the functions and outputs of these circuits and how they are used in digital systems.
