Fordham, New York City's Jesuit University
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Fordham College Lincoln Center Computer Organization
Dept. of Computer and Info. Science Spring, 2005

Homework Assignment 4
Due date: February 22

[10] $<$§B.10$>$ A friend would like you to build an ``electronic eye'' for use as a fake security device. The device consists of three lights lined up in a row, controlled by the outputs Left, Middle, and Right, which, if asserted, indicate that a light should be on. Only one light is on at a time, and the light ``moves'' from left to right and then from right to left, thus scaring away thieves who believe that the device is monitoring their activity. Draw the graphical representation [state diagram] for the finite state machine used to specify the electronic eye. Note that the rate of the eye's movement will be controlled by the clock speed (which should not be too great) and that there are no inputs.

[15] $<$§B.10$>$ Write down the state table and output table for the finite state machine you constructed for Exercise B.37. Assign state numbers to the states of this machine, and derive a set of logic equations for the next state bits (assuming D flip-flops are used) and the external outputs that control the lights. Simplify the equations as much as you can.

[25] $<$§B.10$>$ We wish to add a yellow (amber) light to our traffic light example on page B-68. We will do this by changing the clock to run at 0.25 Hz, corresponding to a 4-second clock cycle time, which is the duration of a yellow light. To prevent the green and red lights from cycling too fast, we add a 30-second timer. The timer has a single input, called TimerReset, which restarts the timer, and a single output, called TimerSignal, which indicates that the 30-second period has expired. The timer signal is used as an input to control the transitions from one state to another. Also, we must redefine the traffic signals to include yellow. We do this by defining two output signals for each light: green and yellow. If the output NSgreen is asserted, the green light is on; if the output NSyellow is asserted, the yellow light is on. If both signals are off, the red light is on. Do not assert both the green and yellow signals at the same time. The same scheme is used for the EW lights. Draw the graphical representation for the finite state machine for this improved controller. Choose names for the states that are different from the names of the outputs.

[15] $<$§B.10$>$ Write down the next-state and output-function tables for the traffic light controller described in Exercise B.41.

[15] $<$§B.10$>$ Assign state numbers to the states in the traffic light example of Exercise B.41 and rewrite the tables of Exercise B.42 as truth tables. Use these truth tables to write a set of logic equations for each of the outputs, including the next-state outputs (assuming D flip-flops are used).

Robert Moniot 2005-02-14