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Questions and Answers
What distinguishes sequential circuits from combinational circuits?
What distinguishes sequential circuits from combinational circuits?
- Sequential circuits depend only on current input.
- Sequential circuits do not use flip-flops.
- Sequential circuits output depends on previous inputs. (correct)
- Combinational logic can model time-dependent conditions.
What is used to represent the current and next conditions of a flip-flop in sequential circuits?
What is used to represent the current and next conditions of a flip-flop in sequential circuits?
- X(t) and X(t+1)
- B(t) and B(t+1)
- A(t) and A(t+1) (correct)
- C(t) and C(t+1)
What is the primary purpose of excitation tables in the design of sequential circuits?
What is the primary purpose of excitation tables in the design of sequential circuits?
- To establish a circuit specification
- To provide transition characteristics between current and next states (correct)
- To conduct state reduction operations
- To create a state diagram
Which of the following structures is used to analyze the behavior of a sequential circuit?
Which of the following structures is used to analyze the behavior of a sequential circuit?
What do state tables in sequential circuits resemble?
What do state tables in sequential circuits resemble?
Which step is not included in the design process of a sequential circuit as per the content provided?
Which step is not included in the design process of a sequential circuit as per the content provided?
How many lines does a state table require if there are M flip-flops and N inputs?
How many lines does a state table require if there are M flip-flops and N inputs?
In designing a circuit using JK flip-flops, what is the initial action to take?
In designing a circuit using JK flip-flops, what is the initial action to take?
What can sequential circuits model that combinational circuits cannot?
What can sequential circuits model that combinational circuits cannot?
What must be determined after building the state table during the design of a sequential circuit?
What must be determined after building the state table during the design of a sequential circuit?
From which of the following materials does one start when building an excitation and output table?
From which of the following materials does one start when building an excitation and output table?
Which component is essential for sequential circuits to hold previous states?
Which component is essential for sequential circuits to hold previous states?
In sequential circuit design, what is the purpose of a state equation?
In sequential circuit design, what is the purpose of a state equation?
What aspect characterizes the circuit specification essential for sequential circuit design?
What aspect characterizes the circuit specification essential for sequential circuit design?
Which of the following elements is essential in linking current conditions to future conditions in flip-flops?
Which of the following elements is essential in linking current conditions to future conditions in flip-flops?
What should be included in the design of a circuit when transitioning from a state table to a logic diagram?
What should be included in the design of a circuit when transitioning from a state table to a logic diagram?
What does each arrow in a state diagram represent?
What does each arrow in a state diagram represent?
How many states does a circuit with m flip-flops have?
How many states does a circuit with m flip-flops have?
In the expression y = (A+B)x’, what does y represent?
In the expression y = (A+B)x’, what does y represent?
What is the function of the flip-flop input function?
What is the function of the flip-flop input function?
Which flip-flop types use two characters to represent their inputs?
Which flip-flop types use two characters to represent their inputs?
What is the role of a criteria table for flip-flops?
What is the role of a criteria table for flip-flops?
Which component is specifically used in Example 2 to illustrate flip-flop inputs?
Which component is specifically used in Example 2 to illustrate flip-flop inputs?
To derive the input flip-flop function, what information is necessary?
To derive the input flip-flop function, what information is necessary?
Flashcards
Sequential Circuit?
Sequential Circuit?
Circuit whose output depends not only on the current input but also on the past history of inputs (previous states). They 'remember' past inputs.
Combinational Logic
Combinational Logic
Logic that uses only the current input to decide the output. It doesn't 'remember' past inputs.
State Table
State Table
A representation of a sequential circuit's behavior in table form. Shows what happens to the circuit based on current state and input.
State Diagram
State Diagram
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State Equation
State Equation
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Output Function
Output Function
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Current Condition
Current Condition
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Next Condition
Next Condition
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Flip-flop Excitation Table
Flip-flop Excitation Table
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Flip-flop Input Function
Flip-flop Input Function
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State
State
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Arrow in a State Diagram
Arrow in a State Diagram
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Sequential Circuit Output Function
Sequential Circuit Output Function
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Sequential Circuit Analysis
Sequential Circuit Analysis
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Study Notes
Sequential Circuit Design
- Sequential circuits have an additional dimension: time.
- Combinational logic depends only on the current input.
- Sequential circuits depend on both current and previous inputs.
- Sequential circuits are more powerful than combinational logic.
- Sequential circuits can model conditions not possible in combinational logic.
Sequential Circuit Analysis
- To analyze a sequential circuit, start with a diagram.
- Determine the flip-flop inputs and outputs.
- Use A(t) and A(t+1) for current and next conditions.
- An alternative method uses A and A+ to represent current and next conditions of flip-flops.
- Example 1 uses a D flip-flop:
- A+ = A â‹… x + B â‹… x
- B+ = A' â‹… x
- y = (A + B) â‹… x'
Sequential Circuit Analysis (Continued)
- Derive a state table from state and output functions.
- The state table is similar to a truth table.
- State table:
- Input and conditions appear on the left.
- Outputs and next conditions appear on the right.
- M flip-flops and n inputs create 2m+n combinations.
Sequential Circuit Analysis (Example 1)
-
State Equations
- A+ = A â‹… x + B â‹… x
- B+ = A' â‹… x
-
Output Function
- y = (A + B) â‹… x'
Flip-Flop Input Function
- Sequential circuit output depends on flip-flop current state and input.
- Example 1: y = (A + B) â‹… x'
- Circuit sections generating flip-flop input are described by flip-flop input equations (using algebra).
Flip-Flop Input Function (Continued)
- Flip-flop input functions determine the next condition.
- Use criteria tables for flip-flops to find the next condition for each flip-flop from the function.
- Example 2 uses JK flip-flops:
- JA = B â‹… Cx + B' â‹… Cx'
- KA = B + y
Analysis: Example 3
- Given a sequential circuit with two JK flip-flops (A and B) and one input (x):
- Determine the flip-flop input functions:
- JA = B
- KA = B â‹… x'
- JB = x'
- KB = A' â‹… x + A â‹… x' = A + x
Analysis: Example 3 (Continued)
- Create a state table using flip-flop criteria table to find next state values from input and present state.
- Based on this state table, create a state diagram
Analysis: Example 3 (Continued)
- Draw a state diagram from the state table
- Find the flip-flop input function, and use a criteria table for the flip-flops
Flip-Flop Excitation Tables
- Excitation tables show transition characteristics between current and next conditions to determine flip-flop input values.
- Tables are provided for JK, SR, D, and T flip-flops.
Designing Sequential Circuits
- Circuit design steps start with specifications.
- Create a state table.
- State reduction (if necessary).
- State assignment.
- Flip-flop count determination.
- Excitation and output tables from the state table.
- Circuit output function and flip-flop input function.
- Logic diagram drawing.
Design: Example 1
- Design a sequential circuit using JK flip-flops based on a given state diagram.
- Create a state/excitation table.
Design: Example 1 (Continued)
- Construct a block diagram for the design.
Design: Example 1 (Continued)
- Determine flip-flop inputs from the state table.
Design: Example 2
- Design a sequential circuit using D flip-flops based on a given state table
Design: Example 2 (Continued)
- Determine input expressions for flip-flops and output.
- Use the input expressions to create a logic diagram
Design a Synchronous Counter
- Binary counters count through a binary sequence.
- n-bit counters count from 0 to 2n − 1.
Design a Synchronous Counter (Example 1)
- 3-bit binary counter using T flip-flops.
- A state diagram and a table showing the next state and flip-flop inputs are created.
Design a Synchronous Counter (Continued)
- Develop equations for the flip-flop inputs (TA2, TA1, TA0).
- Construct a logic diagram of the 3-bit binary counter.
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