Page 151 - Bebop to The Boolean Boogie An Unconventional Guide to Electronics Fundamentals, Components, and Processes

732 rn Chapter Twelve

Every time the controller inspects the nickel and dime signals, it sends an
acknowledge signal back to the receiver. The acknowledge signal informs the
receiver that the coin has been accounted for, and the receiver responds by
resetting the nickel and dime signals to 0 and awaiting the next coin. The
acknowledge signal can be generated in a variety of ways which are not
particularly relevant here.
When the controller decides that sufficient funds have been deposited,
it instructs the dispenser to dispense a “gizmo” and any change (if necessary)
by setting the dispense and change signals to 1, respectively.

State Diagrams

A useful level of abstraction for a function such as the controller is to
consider it as consisting of a set of states through which it sequences. The
current state depends on the previous stute combined with the previous values on

the nickel and dime inputs. Similarly, the next state depends on the current state
combined with the current values on the nickel and dime inputs. The operation
of the controller may be represented by means of a state diagram, which offers a
way to view the problem and to describe a solution (Figure 12-2).

Figure 12-2. State diagram for the controller