CS 273

Homework 8

Due Wednesday, April 25, 2001

Read text pages 385-393, about the analog input.

Not From the Book

Write a driver for the analog inputs. It should have the following API

Synopsis

unsigned char analog(unsigned char analogno)

Parameter

Valid values are 1 through 8. Specifies which of the analog inputs to read (as with the digital input, there is no equivalent of the broadcast value used for the motor driver)

Return Value

Return 255 on an out-of-range input. Otherwise return the value returned by the analog input.

Known Bug

There won't be any way to distinguish an invalid user input from a value of 255 returned by the sensor. It's very unusual to get a value of 255 if there is actually a sensor attached to the analog port, so this is not a serious problem.

When the user requests a value, you'll need to

1. Check the user's input
2. Turn on the analog subsystem
3. Request the analog subsystem read the specified port
4. Wait for valid data
5. Read the four values returned for the specified port, and average them.
6. Turn off the analog subsystem.
7. Return the value to the user.

Lab

Wire up two bumpers for your robot. Use the driver I gave you, and the driver you wrote for HW7, to write a program that will go forward unless it hits a wall, and will do obstacle avoidance as discussed in class if it does run into a wall.