Bridge to Logictopia Project Summary

Read this entire specification carefully. Like a specification you will receive in industry, the

information is spread out and not necessarily organized as you might expect. An important item

might be buried in the middle of a paragraph where it is not expected. As you are responsible for

meeting all the requirements, read this document slowly and carefully!

An island off the coast called Logictopia has agreed to permit visitors. Until now, the island has

remained isolated and, in order to limit the number of visitors, has agreed to a narrow footbridge

to connect them with the mainland. Due to the local geography, the nearest coastline is several

hundred meters higher than the closest point of the island. As a result, it takes twice as long to

leave the island as to go to the island. The bridge is so narrow that people going in different

directions cannot pass each other and, therefore, pedestrians may only cross in one direction at a

time. The goal of this project is to design a circuit which indicates whether it is safe for a

pedestrian to start across a bridge.

There are two inputs and two outputs:

Inputs:

D: $0$ means nobody departed the island during this clock cycle; $1$ means a person has departed

$V$ : $0$ means nobody left the mainland to visit the island; $1$ means someone is crossing to visit the

island

Outputs:

L: $0$ means it is unsafe for someone to leave the island; $1$ means it is safe to leave the island

M: $0$ means it is unsafe for someone to leave the mainland; $1$ means it is safe to leave the mainland

You can think of $L$ and $M$ as traffic lights: when $0,$ they are red, when $1,$ they are green. You can

assume that people always obey these traffic lights.

There are rules that the Logictopians insist be followed:

Only one person may start crossing the bridge at a time.

It takes $2$ clocks to go from Logictopia to the mainland.

It takes $1$ clock to go from the mainland to Logictopia.

There may be $2$ people on the bridge at a time if both are leaving Logictopia.

There may only be $1$ person on the bridge going to visit Logictopia.

You may assume that there is another circuit, called the Simultaneity Prevention Insurance

Technology $($aka SPIT$),$ which will prevent $D$ and $V$ both asserting at the same time when there are

no pedestrians on the bridge. $($That means $DV=11$ can be treated as a don't care condition in all

states.$)$ However, you are responsible for doing TWO designs. For your second design, you may add

states to ensure that pedestrians are prevented from entering both directions at once so that no SPIT is

required. A problem with the above specification is there is no rule which says that once pedestrians

start in one direction, the pedestrians traveling in the other direction have to get a chance to cross.

Your second design could, instead, prevent this from occuring by limiting how many can travel in a

row in any one direction.

Come up with ideas on how you'd like to design the system. Interview three different stake

holders to discuss your ideas. Stake holders may be other students, TAs, UGTAs, or family