Mealy vs Moore Machines

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Questions and Answers

What must be true for the OR of all conditions of transitions leaving a state?

It must equal 1. (correct)

It must be exclusively dependent on one variable.

It must equal 0.

It must have at least two true conditions.

Which expression is equivalent to $a + a'b$?

$ab + a'b'$

$a + (a + a')b$ (correct)

$a + 0$

$a + ab$

In the context of transition conditions, what does it indicate if the AND of each pair is always 0?

All conditions are false.

All conditions are true.

Only one condition is true. (correct)

At least one condition is true.

What is the result of the expression $ab' * (a'b' + a'b + ab)$?

$0$ Signup and view all the answers

Which of the following describes a property that must be obeyed by transitions in a finite state machine?

At least one transition condition must always be true. Signup and view all the answers

What does the equation $ar * a' * a(r' + b + g)$ simplify to?

$(a * a')r$ Signup and view all the answers

In the given transitions, which button presses are intuitively represented by $ar * a(r' + b + g)$?

Pressing red and blue simultaneously Signup and view all the answers

How can you state a transition could be true in the context provided?

Two transitions can occur simultaneously Signup and view all the answers

Which flip-flop type is noted for use in this course?

D-FF Signup and view all the answers

What is one of the first steps in the design process using FSMs?

Determine what needs to be remembered Signup and view all the answers

In the equation $ar(r' + b + g)$, what does it indicate if a transition fails?

It implies that $ar$ should be $arb'g'$ Signup and view all the answers

What does the note about the author imply regarding the pitfall mentioned?

It is a common pitfall in design Signup and view all the answers

In the equation $0 + arb + arg$, what happens to the transitions when the output is zero?

None of the transitions trigger Signup and view all the answers

What is the primary function of the described synchronous sequential machine?

To detect a specific sequence of input pairs. Signup and view all the answers

Which model is used to represent the machine that outputs based on current and previous states?

Mealy model Signup and view all the answers

In the state transition table of the Mealy model, what is the output when in state 4 and the input is 10?

0 Signup and view all the answers

How many unique states are defined in the Moore model's state transition table?

5 Signup and view all the answers

What happens to redundant states in the state diagram of the machine?

They should be eliminated to simplify the design. Signup and view all the answers

Which state does the machine transition to when in state 3 with inputs 11 in the Moore model?

State 3 Signup and view all the answers

Which input pair results in the machine outputting 1 in the Mealy model?

10 Signup and view all the answers

What is the output for the input pair 00 in state 2 of the Mealy model?

0 Signup and view all the answers

What happens when the finite state machine enters an unused state?

It will not transition to a valid state Signup and view all the answers

What is the state of the finite state machine when U=0?

The counter retains its previous value Signup and view all the answers

Which of the following represents the unused states in the modulo 6 counter?

110 and 111 Signup and view all the answers

What should be done with the unused states to handle them effectively?

Create dummy states that redirect to known outcomes Signup and view all the answers

What indicates that the machine is in an invalid state?

Output values display C=0 and 111 Signup and view all the answers

In the revised modulo 6 counter diagram, what happens when the present state is 110?

The next state is 110 if U=0 or 111 if U=1 Signup and view all the answers

What is a condition that leads to the FSM being in an unused state upon power-up?

Improper initial state configuration Signup and view all the answers

What is a key aspect of the transition from an unused state to a valid state in the modulo 6 counter?

Dummy states redirect to a known state on the next cycle Signup and view all the answers

What is a key characteristic of Mealy machines?

Outputs can change independently of the clock. Signup and view all the answers

What advantage do Moore machines have over Mealy machines?

They eliminate glitches in outputs. Signup and view all the answers

What must occur to eliminate glitches in a Mealy machine?

Synchronize the Mealy outputs with storage elements. Signup and view all the answers

In the context of the FSM example for a secure car key, what triggers the transmission of the ID?

The car's computer requests the identifier. Signup and view all the answers

What is the output value 'r' during the 'Wait' state in the secure car key FSM?

0 Signup and view all the answers

What happens if an incorrect button is pressed in the FSM for the code detector?

The FSM resets to the 'Wait' state. Signup and view all the answers

In what order must the buttons be pressed in the code detector FSM?

Start, Red, Blue, Green Signup and view all the answers

Why might some designers prefer using Mealy machines?

They have fewer states than Moore machines. Signup and view all the answers

What is the output 'u' of the FSM in the code detector when the sequence is completed successfully?

1 Signup and view all the answers

Which of the following best describes how synchronization is achieved in Mealy machines?

By introducing storage elements. Signup and view all the answers

Which FSM state indicates that no button has been pressed yet in the code detector?

Wait Signup and view all the answers

How does the output of the Mealy machine compare to that of the Moore machine?

Moore outputs produce glitch-free results. Signup and view all the answers

What is the purpose of timing diagrams in FSM designs?

To evaluate output behavior for different input sequences. Signup and view all the answers

Which state must be reached after the 'Start' state in the code detector FSM?

Red1 Signup and view all the answers

The Moore model's outputs are dependent on the current input variables.

False Signup and view all the answers

Mealy machines tend to require more states than Moore machines due to their output functions being dependent on both state and input.

False Signup and view all the answers

In the Moore model, outputs change asynchronously with state transitions and clock edges.

False Signup and view all the answers

The output functions of the Moore machine are simpler than those of the Mealy machine, as they are based solely on states.

True Signup and view all the answers

Both Mealy and Moore machines use the same state diagram structure for illustrating their functionality.

False Signup and view all the answers

The Mealy model provides outputs that are triggered based on the state transition process.

True Signup and view all the answers

Transitions in a Moore machine are labeled with output conditions instead of input combinations.

False Signup and view all the answers

A Mealy machine's outputs can change immediately with changes in input conditions while in the same state.

True Signup and view all the answers

The unused states for the modulo 6 counter are 110 and 111.

True Signup and view all the answers

Whenever U=1, the state counter will always increment.

False Signup and view all the answers

The modulo 6 counter can enter an invalid state upon power-up.

True Signup and view all the answers

Creating dummy states can help ensure the FSM transitions to known states.

True Signup and view all the answers

If the current state is 111 and U=1, the next state will also be 111.

False Signup and view all the answers

A state diagram specifies all transitions for every possible input combination.

True Signup and view all the answers

The output value C=0 indicates the FSM is in a valid state.

False Signup and view all the answers

Incrementing the counter when the state is 101 leads to the desired state of 000.

False Signup and view all the answers

Mealy machines have a synchronous design methodology.

False Signup and view all the answers

Moore machines are known for producing glitch-free outputs.

True Signup and view all the answers

To convert a Mealy machine to a Moore machine, synchronization is required.

True Signup and view all the answers

The outputs of Mealy machines can change in response to input changes regardless of the clock.

True Signup and view all the answers

A code detector FSM opens the door when any button is pressed.

False Signup and view all the answers

In a synchronous Mealy machine, every output is dependent on the current state and inputs.

False Signup and view all the answers

The secure car key FSM transmits its identifier when the computer requests it.

True Signup and view all the answers

If an incorrect button is pressed in the code detector FSM, the sequence is terminated.

False Signup and view all the answers

The input identifier transmitted by the secure car key FSM is always a 4-bit number.

True Signup and view all the answers

If a Mealy machine is modified to eliminate glitches, it remains a Mealy machine.

False Signup and view all the answers

The start button is a critical input in the FSM for the code detector.

True Signup and view all the answers

Synchronous Mealy machines do not require clock signals for their operation.

False Signup and view all the answers

Moore machines tend to have more states compared to Mealy machines.

False Signup and view all the answers

Outputs of a FSM depend on both its current state and previous inputs.

True Signup and view all the answers

A modulo 6 counter uses the binary value 110 in its counting sequence.

False Signup and view all the answers

In a Moore machine, the outputs are generated solely from the current state.

True Signup and view all the answers

When the input U is set to 0, the modulo 6 counter increments its value.

False Signup and view all the answers

The value of the modulo 6 counter is represented as a 2-bit value.

False Signup and view all the answers

A Moore model outputs based solely on the current state of the machine.

True Signup and view all the answers

The output C of the modulo 6 counter is 1 when the counter transitions from state 5 to state 0.

True Signup and view all the answers

In a finite state machine's state transition table, each present state can have multiple outputs for a given pair of inputs.

False Signup and view all the answers

A decoder generates the next state logic for the modulo 6 counter.

True Signup and view all the answers

In a Mealy machine, the outputs are influenced by both the state and the system inputs.

True Signup and view all the answers

The combination of inputs 00 and 10 in state 2 of the Mealy model results in an output of 1.

False Signup and view all the answers

Redundant states in a state diagram should be removed for efficient implementation of a sequential machine.

True Signup and view all the answers

The output value of a modulo 6 counter is always 0 to 5.

True Signup and view all the answers

The next state of the modulo 6 counter can only be generated when U is set to 1.

True Signup and view all the answers

The output of the Moore machine for state 5 and inputs 01 is 1.

True Signup and view all the answers

The transition conditions for the modulo 6 counter involve examining all possible input values.

True Signup and view all the answers

The Mealy model's output is contingent on both the current state and inputs while Moore models rely solely on the inputs.

False Signup and view all the answers

A synchronous sequential machine is designed to detect a specific pattern of input occurrences.

True Signup and view all the answers

The state transition from state 1 to state 2 with input 00 produces an output of 1 in the Mealy model.

False Signup and view all the answers

Study Notes

Mealy vs Moore Machines

Mealy machines have asynchronous outputs which change in response to input changes, independent of a clock.
Moore machines have a more disciplined timing methodology than Mealy machines due to their synchronous outputs.
Traditionally, Mealy models are used for synchronous design, and Moore models are used for asynchronous design.
Mealy machines can have glitches in their outputs due to their asynchronous nature.
Some designers prefer Mealy machines because they can result in fewer states compared to Moore machines.
Moore machines have glitch-free outputs.
To eliminate glitches in a Mealy machine, its output needs to be synchronized, effectively transforming it into a Moore machine.

Synchronous Mealy Machines

Synchronizing a Mealy machine involves breaking the direct connection between inputs and outputs by introducing storage elements.
Storage elements act as a buffer, allowing the system to respond to changes only at designated points.
The clock signal drives the state register and the combinatorial logic responsible for output and next-state determination.

FSM Example: Secure Car Key

Many new car keys incorporate tiny computer chips.
When starting the car, the car's computer (under the hood) requests an identifier from the key.
The key transmits its identifier to the computer in a specific sequence, one bit at a time, using a Finite State Machine (FSM).
The FSM has a set of states (Wait, K1, K2, K3, K4) and responds to the input (a).
If the identifier is incorrect, the computer shuts off the car.

FSM Example: Code Detector

The FSM example is a code detector which unlocks a door only when buttons are pressed in a specific sequence: start, red, blue, green, red.
The FSM waits for the "start" button (s=1) before transitioning to the "start" state.
It then progresses to the "red", "blue", "green", and "red" states in sequence.
Each state corresponds to pressing a specific coloured button.
The FSM uses input signals (s, r, g, b) representing each button and output signal (a) indicating when a coloured button is pressed.
If the correct sequence is followed, the door unlocks (u=1).
If an incorrect button is pressed at any step, the FSM returns to the "Wait" state without unlocking the door.

State Reduction

State tables and diagrams may contain redundant states that can be eliminated to reduce the number of components needed for implementation.
Removing redundant states streamlines the design by reducing the overall complexity.

Unused States

If a finite state machine enters an unused state, a problem can occur with the FSM's functionality.
Unused states, also known as unknown or undefined states, can arise from design flaws or power-up situations.
Unused states can be handled by creating dummy states that transition to a known state on the next clock cycle.

Modulo 6 Counter Analysis

A modulo 6 counter has six states with binary values from 000 to 101.
The counter's state is stored in the state register of the finite state machine's hardware.
Unused states, such as 110 and 111, are not intended to be accessed and can cause unpredictable behavior.
To handle unused states in the modulo 6 counter, dummy states 110 and 111 are created and transition to a known state on the next clock cycle. This ensures that the finite state machine always remains in a valid state.

FSM Design Process

Determine the information to be stored in the FSM's memory.
Encode the inputs and outputs in binary representation, if necessary.
Construct a state diagram to represent the desired behavior of the device.
Assign a binary number (code) to each state.
Choose the type of flip-flop to use.
Derive the flip-flop input maps.
Create the combinational logic equations and draw the schematic based on the equations.

Mealy Machine

Outputs are associated with transitions between states, labeled with both input combinations and output values
Example: "00/0" represents an input of "00" resulting in an output of "0"
Changes in output value occur asynchronously when inputs change, independent of the clock cycle

Moore Machine

Outputs are associated with specific states, labeled with state names
Outputs change synchronously with state transitions with a clock edge
Example: A state named "C" could have an output value of "0", independent of input changes

Moore vs Mealy

Moore machines use a larger number of states to manage output conditions, resulting in simpler output function logic that is independent of input variables
Mealy machines typically require fewer states, but their asynchronous output behavior can lead to glitches
For synchronous design, Mealy machines are common; Moore machines are used for asynchronous design

Synchronous Moore Machine

Mealy machines are often synchronized to eliminate glitches.
The Mealy machine output is connected to storage elements (like flip-flops) with an active clock signal to ensure output synchronization.
Essentially converting the Mealy machine into a Moore machine.

Car Key Secure FSM

Small computer chips in car keys function as finite state machines.
The car's computer requests an identifier from the key during startup.
The key transmits a 4-bit identifier bit-by-bit.
If the identifier matches, the startup sequence completes; if not, the engine shuts off.

Code Detector FSM

Designed to unlock a door (u=1) by a specific sequence of button presses: "start", "red", "blue", "green", "red".
Inputs are: "s" for start, "r" for red, "g" for green, "b" for blue, and "a" for button press.
Outputs are: "u" for unlock and "a" for button press indication.
The FSM starts in a "Wait" state.
An incorrect button sequence results in returning to the "Wait" state and not unlocking the door.

Modulo 6 Counter

A 3-bit counter that cycles through states 000-101.
Input "U" controls counting:
- When U=1, the counter increments on the rising edge of the clock.
- When U=0, the counter retains its value.
Output "C" is 1 for the 101-000 transition, and 0 otherwise.

Modulo 6 Counter State Diagram

In a Moore machine, outputs are represented alongside each state.
Inputs are on the arcs connecting the states.
The state transitions based on the input "U".

FSM with Counter and Decoder

The counter acts as a register for storing the current state and also contributes to the next state logic.
The counter output drives a decoder, with each decoder output representing a specific state.
Combinational logic uses inputs and decoder outputs to generate both system outputs and next-state information.
A Mealy machine is implemented when inputs are used to direct both the next state and system outputs.
A Moore machine arises when outputs only rely on the state value, and inputs only control the next state transition.

Unused States in FSMs

FSMs that are not in a known/valid state are considered to be in an unused state.
This can occur during power-up or due to design flaws.
Unused states may prevent the FSM from reaching a valid state.

Handling Unused States in Modulo 6 Counter

Implement dummy states to handle unused states (like 110 and 111).
Dummy states transition to a known state on the next clock cycle.
Outputs from dummy states can be used to indicate an error condition.

State Reduction

Redundant states in a state table/diagram can be eliminated, reducing the complexity of the implemented circuit and the number of components used.
Aim is to achieve transitions to the same state from different combinations of input values without always going through the same state.

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Description

This quiz explores the key differences between Mealy and Moore machines, including their output behaviors and synchronization methods. You'll learn about the advantages and disadvantages of each type, as well as the implications for design choices in synchronous and asynchronous environments.