Aaron's Bicycle Light

Tom Kelliher, CS 240

Mar. 5, 1999

Administrivia

Announcements

Review Monday. Midterm Wednesday.

From now on, assigned readings will be classified as covered material or background material. At the beginning of the next class I will ask for questions on the background material. Other than answering those questions, we will not discuss the background material in class.

You are responsible for reading the background material before class.

Assignment

For next Friday.

Background material: Section 5.1 minus An Overview of the Implementation.

Covered material: An Overview of the Implementation, Section 5.2.

From Last Time

D flip-flop.

Outline

1. Design of a state machine.

Coming Up

Simple MIPS datapath.

Bicycle Light Design Example

The product: a bicycle light which has a button and a number of LEDs. Push the button once and the LEDs shine steadily. Push again and it goes off. Push a third time and the LEDs flash on and off a few times a second. Push one more time and it goes off again.

Design steps:

1. Determination of inputs and outputs.

2. Determination of machine states.

3. Transition assignment.

4. State assignment.

5. Truth tables.

6. Implementation.

Questions along the way:

1. How many state bits?

2. The state assignment problem. In this case: simplify LED equation.

3. What to do with unused states? Don't cares; or do we care?

4. What clock frequency? Issues: design simplification, power consumption.

5. An alternative: one-hot state machines.