Design a sequential circuit using D-flip flops for a simple candy machine controller. The candy machine...

 

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Design a sequential circuit using D-flip flops for a simple candy machine controller. The candy machine must release a candy after 15 cents are deposited. It has a single coin slot for dimes (10 cents) and nickles (5 cents). It gives no change. The circuit must have two inputs (N for "nickel is deposited" and D for "dime is deposited"), and one output OPEN (1 for "release a candy" and 0 for "closed"). Two coins cannot be inserted simultaneously. You may assume that the N and D signals are produced by the sensor in such a way that they are asserted (ie, become 1) for a very short duration that includes just one active clock edge. That is, a single coin can only cause one state transition. (Hint: You can do this with as few as four states!) i) Derive the state diagram for a Moore-type system. Use whatever you determine in this step for parts (ii) and (iii). (Note: If you are unable to come up with a suitable solution for this part, give a state diagram for any reasonable four-state two-input system to complete parts (ii) and (iii)) [10 marks] ii) Assign the necessary number of bits (for example, using variable names Q and Qo) to represent the states of the system. Create the state table that defines the two input variables N, D, the current-states, next-states, and the output OPEN. Use don't cares where appropriate. [5 marks] iii) Implement the system using D flip-flops and whatever combinational gates you may need, and sketch the circuit. [5 marks] Design a sequential circuit using D-flip flops for a simple candy machine controller. The candy machine must release a candy after 15 cents are deposited. It has a single coin slot for dimes (10 cents) and nickles (5 cents). It gives no change. The circuit must have two inputs (N for "nickel is deposited" and D for "dime is deposited"), and one output OPEN (1 for "release a candy" and 0 for "closed"). Two coins cannot be inserted simultaneously. You may assume that the N and D signals are produced by the sensor in such a way that they are asserted (ie, become 1) for a very short duration that includes just one active clock edge. That is, a single coin can only cause one state transition. (Hint: You can do this with as few as four states!) i) Derive the state diagram for a Moore-type system. Use whatever you determine in this step for parts (ii) and (iii). (Note: If you are unable to come up with a suitable solution for this part, give a state diagram for any reasonable four-state two-input system to complete parts (ii) and (iii)) [10 marks] ii) Assign the necessary number of bits (for example, using variable names Q and Qo) to represent the states of the system. Create the state table that defines the two input variables N, D, the current-states, next-states, and the output OPEN. Use don't cares where appropriate. [5 marks] iii) Implement the system using D flip-flops and whatever combinational gates you may need, and sketch the circuit. [5 marks]

Answer rating: 100% (QA)

State Diagram State A No coin deposited N0 D0 Stay in state A OPEN0 N0 D1 Move to state B OPEN0 N1 D... View the full answer