Digital System Issues Analysis - Assignment Example

The data input goes through when the gate or enable input is on, which means that it is transparent when the gate is on. D flip-flops are found in integrated circuits, usually with multiple latches per circuit. For example, D flip-flops have been used in the 7400 series of integrated circuits.

In the figure, the input D is shown, with the out displayed in ‘Q’. This is how the input and to put to give the necessary output in such a flip-flop.

The Algorithmic State Machine (ASM) is a method that is used to design finite state machines. It is used to show diagrams of digital integrated circuits. The ASM diagram is like a state diagram but less formal and thus easier to understand. State machines are functional forms of application planning. When an application is developed, its complexity also increases, state machine diagrams help to accommodate such complexities in the design easily. Creating an effective State Machine requires the designer to make a table of all possible states. With this table, the designer can plan how each state is related to another. The design process involved in creating an operative State Machine will also improve the overall design of the application.

The proposed application has the following requirements:
- The coke products are sold for 50 cents.
- The machine can accept only nickels, dimes, and quarters.
- The exact amount of change is not needed.
- Change can be returned at any time, during the process of entering coins.

In the above figure of the state diagram for the coke application, there are eight states, which are as follows:
- INIT – initialize our Coke Machine;
- WAIT FOR EVENT – where the machine waits for coins;
- RETURN CHANGE – where the machine returns change;
- COKE PRODUCT – when the machine has received 50 or more cents it will dispense the beverage;
- QUARTER – when the customer enters a quarter;
- DIME – when the customer enters a dime;
- NICKLE – when the customer enters a nickel;
- EXIT – after the change is returned and/or beverage dispensed, the machine will power down (application will terminate).

If the above application has to work without problems, the design must be kept as simple as possible and it must be modular. It is important to implement one module at a time and test each module. While building the design, it is important to be aware of clock skew and use similar path lengths to all flip-flops. Gated clocks, must be avoided and all positive-edge-triggered or all negative-edge-triggered flip-flops must be used in the design.

It is important to keep track of asynchronous inputs to the circuit and better to avoid such inputs altogether. If such inputs cannot be avoided, it is better to synchronize them.  The use of debounced switches will help to provide clean input signals. All flip-flops must be initialized to known values at the beginning and the dependencies on minimum logic gate delays must be avoided.