CS-424, Lab # 4
Microcontroller Digital I/O Ports
2-20-09, Report Due: 2-27-09
In this lab you will use PIC18F452 microcontroller digital I/O ports to
control external circuitry you design and build on the QuikProto board.
You will also design and build an entire micontroller-based microcomputer
on the proto board using a PIC16F84A microcontroller chip. You will use
an EPIC PROM Programmer to program the PIC16F84A to control external
circuitry.
Part 1. The Hardware
In this part of the experiment you are to wire up circuitry on the
QuikProto board that will display the states (open or closed) of four
DIP switches on four light emitting diodes. Whenever any switch is
closed, the corresponding LED should come on; it should be off when the
switch is open. Wire up four of the leads of an 8-position DIP switch
between +5 volts and ground through a 10K resister. Connect this
circuitry to bits PC0-PC3 of PORTC of the PIC18F452 that have been
brought over to the proto board from the QuikFlash board. The wiring
should be done in such a way that when the switch is open +5 volts is
input to the port and when it is closed, 0 volts (ground) goes to the
port. (Use the wiring of switch SW3 in the QuikFlash board schematic on
Page 332 of your text book as a guide.) Connect each of four LEDs in
series with four 1K resistors to bits PB0-PB3 of PORTB of the PIC18F452
that have been brought over to the proto board, so that the LEDs are
either turned on or off depending on the value of the bit stored in the
port. Note that there are two ways of doing this: either by connecting
to +5 volts or to ground. (Again refer to the schematic on page 332 of
your text, concentrating on diodes D2, D4, D5, and D6.) When you wire
up this part of the circuit be sure that you get the polarity of the
LEDs right. (The flat side of the LED with the shorter of the two wires
is the cathode--the side that corresponds to the vertical line and NOT
the triangle on the LED schematic symbol.) This is very important,
since if you wire the LEDs backwards, they could literally blow up on
you!! Before you apply power to the board, be sure you show your
circuit to the lab instructor.
Be sure to leave at least nine consecutive positions on the
protoboard free. You will need these for Part 2 of the experiment.
The Software
A. Write a program that will configure PORTB and PORTC correctly, turn
off all of the LEDs, and then continually read the switches and send
their bit pattern to the output port, thereby displaying them on the
LEDs.
B. Write another program that does different things when different
switches are closed. Specifically: if the switch that's connected to PC0
is closed, all the LEDs should be turned off; if the one connected to PC1
is closed, all the LEDs should be turned on; if the one connected to PC2
is closed, the LEDs should simultaneously blink on and off; if the one
connected to PC3 is closed, the PB0 LED should be lit and turned off,
then the PB1 LED, then the PB2, LED, then the PB3 LED. This action
should continue until a different switch is closed. For this part you
may assume that only one switch at a time is closed. Demonstrate to the
lab instructor that everything is working correctly.
Part 2.
In this part of the experiment you are to use a different microcontroller
(the PIC16F84A) to control the same hardware you wired up on the proto
board in Part 1.
The Hardware
Insert a PIC16F84A microcontroller into the protoboard so that its pins
occupy the nine consecutive positions you left available in Part 1. Use
extreme caution when you insert the PIC16F84A into the protoboard. Its
pins are very fragile and easily broken. Wire up the PIC16F84A "Core
Circuit" shown in the following diagram. Here VCC is the same as VDD
(+5 volts) brought over to the protoboard from the QuikFlash board; VSS
is ground (also brought over from the QuikFlash). Be sure to get the
polarity of the tantalum capacitor correct.
Connect the four DIP switches and the four LEDs from Part 1 of the
experiment to bits RA0-RA3 of PORTA and bits RB0-RB3 of PORTB of the
PIC16F84A, respectively. For the pin numbers of those port bits you
should refer to the PIC16F84A data sheet (available from the
Microchip.com web site:
http://ww1.microchip.com/downloads/en/DeviceDoc/35007b.pdf).
The Software
Use MPLAB to develop an assembly language program for the PIC16F84A that
will perform the same task as in Part A of the first section of this lab.
(PORT A will now be the input port.) Be sure that you set the MPLAB
configuration for the PIC16F84. You will again need to refer to that
microcontroller's data sheet to see how to configure the two ports for
input or output. The process is a bit more complex than for the PIC18F452.
Basically, to get access to the memory bank that contains TRISA and TRISB
(the tristates that control the direction of the ports), you need to
manipulate the RP0 bit of the STATUS register: If that bit is set,
subsequent memory accesses will be to "Bank 1", which contains TRISA and
TRISB; if the bit is cleared, subsequent accesses will be to "Bank 0",
which contains PORTA and PORTB. As for the PIC18F452, setting any bit in
TRISA or TRISB programs the corresponding port for input; clearing a bit
programs it for output. You will also need to have the following lines at
the start of your program:
#include "P16F84.inc"
__CONFIG_CP_OFF & _WDT_OFF & _XT_OSC & _PWRTE_ON
Once the program is developed and built, use the EPIC programmer to
"burn" the program into the microcontroller's flash program memory.
To do this, carefully remove the PIC16F84A from the protoboard. Once
again, the pins of the PIC16F84A are quite fragile and easily broken, so
use a chip remover or a small screwdriver to very slowly and carefully pry
the chip out of the protoboard. Carefully insert it into the programmer's
IC socket and connect the programmer to the PC's parallel port using the
provided cable. Start the EPICWIN program and refer to the "Help" to learn
how to use the programmer. Once the program is downloaded, very carefully
remove the microcontroller from the EPIC's socket and place it back into
the protoboard. Apply power and you should be able to change the switch
settings and observe the results on the LEDs. Show the working system to
the lab instructor.
Lab Report
Your lab report should contain detailed diagrams of all circuits developed
and implemented in this lab as well as the assembled listings (.LST) and
.HEX files of all of your programs.