ECE-3120
Spring 2008
LAB 7 – Parallel I/O, part 2
3/26/08 Page 1 of 4 Lab 7
The purpose of this lab is to learn the use of the 68HCS12 parallel ports to interface to
simple devices, in a program that counts and displays switch activations on the LEDs and
7-segment digits. This is a continuation of the program started in Lab 6.
PRE-LAB:
Prepare pseudocode and the first draft of the program. This must be completed before
coming to the lab and shown to the lab instructor at the start of the lab session. Note: The
Pre-Lab must be typed into a proper *.ASM source file, following our standard Program
Format requirements.
Approved: Lab TA _____________________ Date ____________
PROGRAMMING ASSIGNMENT:
Write a fully-commented program for the Dragon12 board, following our standard
Program Format requirements
(http://iweb.tntech.edu/rhaggard/3120s08/Program_Format.htm), including appropriate
directives and labels for memory operands and constants, called Digits.asm. The
program should do the following:
• This program will run forever in a loop, as most real embedded systems do.
So run the program continuously and never exit, except when the reset button
is pressed or power is cycled off-on.
• The LEDs and 7-segment Digits must be time-multiplexed (periodic scanning)
over a suitable timing interval, as discussed in class and in the book. Thus all
Digits and LEDs will always display the proper values, with sufficient
brightness, without any visible flicker.
• (from Lab6) Read the changes in value of two pushbutton switches (labeled
on-board as SW2 and SW5) reliably. So the switches must be de-bounced and
edge-detected so that one and only one count event is produced each time the
switch is pressed, no matter how long it is between pressing and releasing the
switch.
