CSE 477

CSE477 Mid-term Exam (11 February)

Please read through the entire examination first! This exam was designed to be completed in 50 minutes. There are 3 problems as well as some required questions about your project for a total of 100 points. The point value of each problem is indicated in the table below.

Each problem is on a separate sheet of paper. Write you answer neatly in the space provided. Do not use any other paper to hand in your answers.

This exam is OPEN BOOK and OPEN NOTES only your own, of course.

Good luck.

Name:

Problem Max Score Score

1 30

2 30

3 30

4 10

TOTAL 100

1. Microcontrollers and Interfacing (30 points)

You have a PWM signal as an input to your microcontroller. Your task is to compute the average duty cycle for a sliding window of 10 periods. You do not have any information about the period of the signal except that it is within the range that can be handled comfortably by your microcontroller. Provide pseudo-code for a routine or routines that make use of the input capture facilities of the 68HC11 to perform this computation. Do not worry about scaling the average to any particular units.

2. Microcontrollers and Timers (30 points)

You have to write control software for a mechanical system that requires that 3 tasks be executed with a frequency of 30, 50, and 70ms. Each task takes less than 3ms to execute.

Write pseudo-code for a routine or routines that will perform this task.
How would the structure of your program change if a fourth task with a period of 110ms is added to the other 3. Do not bother writing pseudo-code for this, just describe how the program would be changed.
Do you foresee any complications if the execution time of the original 3 task system were 10ms instead of 3ms? What would you do to deal with them?

3. Serial Communication (30 points)

You have to design a small box that will connect a single serial port on one PC to two devices rather than just one. You are only going to send ASCII data (requiring only 7 bits for each character). The box will consist of a microcontroller with three serial ports (one for the PC and two others for the two devices). How will the PC direct a character to a specific device? How will it know where a character it receives came from? Are there any flow control or arbitration issues to consider? Sketch your approach to designing this box.

4. Project (10 points)

Please list the current unknowns for your final project and your plans for resolving them.

Comments to: cse477-webmaster@cs.washington.edu (Last Update: 02/09/99 )