"Debug" Experiment - Programming and Customizing PICmicro® Microcontrollers







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"Debug" Experiment
For the last experiment, you can try to get this application working.
You should expect the LED connected to RB1 to light and the LED connected to RB0 to
light when the button is pressed. The next page gives the solution to the
problems in this application. The circuit is:

The parts needed for this experiment are listed in the table:


Part
Description


PICmicro® MCU
PIC16F84-04/P


Vdd/Vss Decoupling Capacitor
0.1 uF (Any Type)


_MCLR Pull Up Resistor
10K, 1/4 Watt


4 MHz Ceramic Resonator
Three Leaded Ceramic Resonator with Built in 27-33pF Capacitors


RA0 Pull Up
10K, 1/4 Watt


RA0 Push Button
Momentary On/Modified for Breadboard


RB0 LED Current Limiting Resistor
220W, 1/4 Watt


RB0 LED
Any Type


RB1 LED Current Limiting Resistor
220W, 1/4 Watt


RB1 LED
Any Type


Breadboard
Any Type


+5 Volt "Vcc" Power Supply
Any Type


Using a breadboard, the experiment is wired using the guide:

The source code listed below can be accessed from the
CD-ROM by clicking Here.

title "debug - An application with a few problems"
;
; This is an application to demonstrate how insidious some problems
; can be. This application should be burned into a PICmicro after
; assembly to see if the problems built into it can be found.
;
; The application is *supposed* to turn on a LED at RB1 and wait for
; a button to be pressed. When it is, an LED at RB0 should be turned
; on as well.
;
; Hardware Notes:
; PIC16F84 running at 4 MHz
; _MCLR is tied through a 4.7K Resistor to Vcc and PWRT is Enabled
; A 220 Ohm Resistor and LED is attached to PORTB.0/PORTB.1 and Vcc
; A 10K pull up is connected to RA0 with a Momentary on Switch
;
; Myke Predko
; 99.12.07
;
LIST R=DEC
INCLUDE "p16f84.inc"

; Registers

__CONFIG _CP_OFF & _WDT_ON & _XT_OSC & _PWRTE_ON

PAGE
; Mainline of debug

org 0

nop

movlw 0x001 ; LED at RB1 is On/RB0 is Off
movwf PORTB

bsf STATUS, RP0 ; Goto Bank 1 to set Port Direction
movlw 0x0FC ; Set RB0/RB1 to Output
movwf TRISB ^ 0x090
bcf STATUS, RP0 ; Go back to Bank 0

Loop
btfsc PORTA, 0 ; Wait for RA0 Button to be Pressed
goto Loop

clrf PORTA ; Set RB0 = RB1 = 0 for Both LEDs on

goto Loop ; Loop Forever


end

You will find that this experiment does not work as I outlined above.
There are a number of problems - see if you can find them.
Click Here to look at the corrections to
the problems in this experiment.