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CS 231 Review: Sequential Circuit Design and Counters

CS 231 Review: Sequential Circuit Design and Counters. 28 October 2005. Sequential circuit design procedure. Step 1:

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CS 231 Review: Sequential Circuit Design and Counters

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  1. CS 231 Review: Sequential Circuit Design and Counters 28 October 2005

  2. Sequential circuit design procedure Step 1: Make a state table based on the problem statement. The table should show the present states, inputs, next states and outputs. (It may be easier to find a state diagram first, and then convert that to a table.) Step 2: Assign binary codes to the states in the state table, if you haven’t already. If you have n states, your binary codes will have at least log2 n digits, and your circuit will have at least log2 n flip-flops. Step 3: For each flip-flop and each row of your state table, find the flip-flop input values that are needed to generate the next state from the present state. You can use flip-flop excitation tables here. Step 4: Find simplified equations for the flip-flop inputs and the outputs. Step 5: Build the circuit!

  3. Recognizer • Design a recognizer to recognize possibly overlapping sequences of 110+1+01 • Draw the state table • Use JK flip-flops to implement • Draw the circuit

  4. Sequential Circuit Design • A sequential network is to be used to control the operation of a vending machine which dispenses a $.25 product.The network has three input, N, D, and Q, and two outputs, R and C.The coin detector mechanism in the vending machine is synchronized with the same clock as the sequential network you are to design.The coin detector outputs a single 1 to the N, D, or Q input for every nickel, dime, or quarter, respectively, that the customer inserts. Only one input will be 1 at a time.When the customer has inserted at least $0.25 in any combination of nickels, dimes, and quarters, the vending machine must give change and dispense the product.The coin return mechanism gives change by returning nickels to the customer.For every 1 output on C, the coin return mechanism will return one nickel to the customer.The product is dispensed when the network outputs a single 1 on output R.The network should reset after dispensing the product.

  5. Counter • Design a counter that has the following sequence: 000 -> 011 -> 101 -> 110 -> 111 -> 010 -> 000

  6. Counters • Implement a two-digit, base-4 counter. • Use counters to implement a clock with minutes and hours.

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