Discussion 00 – Tool Installation and Testing

In this exercise, you will validate the installation of the the IDE, the simulator, and assembler (packaged with the compiler).
You will create a simple program that reads the input pins of Port A and replicates those values to Port B.
The program sets all bits of the pin direction control register DDRA to low so that the eight pins of Port A operate as inputs, with the expectation to be driven from an external source.
The program sets all bits of the DDRB register to high so that the eight pins operate as outputs.
PINA refers to the input value of Port A. PORTB refers to the output value being driving to Port B.
You will run this code on a simulator. You will manually manipulate the value of PINA in the simulation, emulate external drive of the physical pins of Port A.

Install

Download and install

  1. MPLAB X
  2. XC8 compiler

MPLAB X : https://www.microchip.com/en-us/tools-resources/develop/mplab-x-ide

alt

XC8 compiler: https://www.microchip.com/en-us/tools-resources/develop/mplab-xc-compilers#tabs

alt

Create Projects Directory

Create a folder to store your projects (each project will live as a sub-directory under this)
In Linux:

mkdir -p ~/MPLABXProjects

Create a Project

Create a project in the projects directory.

In the following example it will be ~/MPLABXProjects/first_cmpe311.X

Start MPLAB IDE
Menu New Project…
Standalone


Toolchain: xc8 compiler


Project Name: first_cmpe311
Check “Set as main project” if not already selected

alt

Create Assembly Source

On the left panel, Right Click Sources
New >
Assembly File .s …

For the file name, use
main

The file extension .s is appended automatically so don’t type main.s

alt

Here are the contents of the file that you should enter.

;; main.s
.equ    PINA    , 0x00
.equ    DDRA    , 0x01
.equ    PORTA   , 0x02

.equ    PINB    , 0x03
.equ    DDRB    , 0x04
.equ    PORTB   , 0x05

.globl main

.org 0x0000

main:
    ldi r16,0x00
    out DDRA, r16 ;set PORTA direction as input
    ldi r16,0xFF 
    out DDRB, r16 ;set PORTB direction as output
loop:
    in  r16, PINA  ;copies input value seen at PORTA to r16
    out PORTB, r16 ;copies r16 to PORTB output
    rjmp loop

Debugging using Manual I/O Interaction

  1. I/O view to setup monitoring and alteration of i/o.
    Menu Window -> Debugging -> I/O View
    Find and Control-Select (Ctrl+LeftMouse) I/O PORT (PORTA) and I/O PORT (PORTB)
  1. Compile and start the debugging session on the simulator

Menu Debug -> Debug Main Project
In main.s, (double) click on a line number within the “main loop” to “break” the execution

Find PortA in the I/O View to alter the input PINA
Set some bits in PINA, or type in a value
Inspect PortB: PORTB…it should be a copy of the valued copied via r16 once you resume

Resume/Step through the program to see the updated output to PORTB

Program memory view

You can view the program memory to see the binary contents. The view will also display what instruction can be interpreted from the memory contents at each location.

Window->Target Memory View-> Program Memory

alt
≡