ECE3120
SPRING 2004
LAB 9 – Parallel I/O Ports
The purpose of this lab is to learn the use of the parallel ports to interface to simple
devices, plus further practice in using subroutines and the Dbug12 monitor functions for
terminal input-output, as applied to a program that counts and displays switch activations.
PRE-LAB:
Prepare pseudocode, the first draft of the program, and a schematic of your I/O interface
circuit. Also draw graphical representations of the stack addresses and contents, as they
should exist during each subroutine execution. This must be completed before coming to
the lab and shown to the lab instructor at the start of the lab session.
Approved: Lab TA _____________________ Date ____________
PROGRAMMING ASSIGNMENT:
1. Build an appropriate I/O circuit and write a fully commented program for the HC12
board, including appropriate directives and labels for memory operands and
constants, called Switch.asm.
You will build, test, and demo this system in the Mechatronics Lab (BN326). Use
your breadboard and components from your EE labs to build the circuit required. The
lab TA will loan you the switches and 7-segment displays for use in the lab, which
must be returned. Wire your breadboard to the HC12 interface adapter board. Be very
careful to use the correct connections! Do NOT use any kind of 7-segment decoder
IC. This system must implement the following functionality:
• Read the changes in value of two toggle switches (called SW1 and SW2)
reliably, using debouncing by the periodic sampling technique as discussed in
class.
• Display a value on two seven-segment LED digits (called DIGIT1 and
DIGIT2), using the scanning technique discussed in class, such that both
digits are always displaying the proper values, with sufficient brightness,
without any visible flicker.
• Light up two LEDs (called LED1 and LED2) as specified below.
• Run the program continuously and never exit, except when the reset button is
pressed or power is cycled off-on.
• Initially reset both transition counts to zero after power-up. Turn off the
DIGITs and LEDs.
4/21/04 Lab 9 1
