Sequential Circuit Design Moore Design Output is a function of - - PowerPoint PPT Presentation

Sequential Circuit Design

Moore Design

Output is a function of present state only

Mealy Design

Output is a function of present state and input

Example

The vending machine delivers a pack of gum after it has received 15 cents in coins. It has a single coin slot that accepts nickels or dimes, one at a time. A mechanical sensor indicates to the FSM whether a nickel or dime has been deposited and it will be asserted every clock period. Implement the system using both Mealy and Moore designs.

Few Assumptions:

• 1. If the customer has deposited two dimes, a single pack of gum will be released and

the remaining nickel is not returned.

• 2. It is not possible to deposit nickel and dime at the same time

Five Steps

• 1. Draw State Diagram [Mealy or Moore as required]
• 2. Do State Assignment
• 3. Draw State Transition Table
• 4. Derive Boolean Expressions
• 5. Draw circuit

STEP 1 : Moore State Diagram

STEP 2 : State Assignment

S0 00 S1 01 S2 10 S3 11

Similarly complete the remaining table

Current State Q1(t), Q0(t) Input D, N Next State Q1(t+1), Q0(t+1) Output Y 00 00 00 00 01 01 00 10 10 00 11 XX 11 00 11 1 11 01 11 1 11 10 11 1 11 11 XX 1

STEP 3: STATE TABLE

STEP 4, 5: Boolean Expressions, Circuit

Using the State table, write the equations in the form

Q0(t+1) = f (Q0(t), Q1(t), N, D) Q1(t+1) = g (Q0(t), Q1(t), N, D) Y = h (Q0(t), Q1(t))

We can follow the same procedure for Mealy Design with few changes

STEP 1,2 : Mealy State Diagram, State Assig.

S0 00 S1 01 S2 10 S3 11

Similarly complete the remaining table

Current State Q1(t), Q0(t) Input D, N Next State Q1(t+1), Q0(t+1) Output Y 00 00 00 00 01 01 00 10 10 00 11 XX X 11 00 11 1 11 01 11 1 11 10 11 1 11 11 XX X

STEP 3: STATE TABLE

STEP 4, 5: Boolean Expressions, Circuit

Using the State table, write the equations in the form

Q0(t+1) = f (Q0(t), Q1(t), N, D) Q1(t+1) = g (Q0(t), Q1(t), N, D) Y = h (Q0(t), Q1(t), N, D)

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