User`s guide

MPLAB

IDE User’s Guide

1.4 LANGUAGE TOOLS

Language tools are programs such as cross-assemblers and cross-compilers. Most

people are familiar with language tools that run on a PC such as Visual Basic or C com-

pilers. When using language tools for embedded systems, a “cross-assembler” or

“cross-compiler” is used. These tools differ from typical compilers in that they run on a

PC but produce code to run on another microprocessor, hence they “cross-compile”

code for a microcontroller that uses an entirely different set of instructions from the PC.

The language tools also produce a debug file that MPLAB IDE uses to correlate the

machine instructions and memory locations with the source code. This bit of integration

allows the MPLAB IDE editor to set breakpoints, allows watch windows to view variable

contents, and lets you single step through the source code, watching the application

execute.

Embedded system language tools also differ somewhat for compilers that run and exe-

cute on a PC because they must be very space conscious. The smaller the code pro-

duced, the better, because that allows the smallest possible memory for the target,

which reduces cost. This means that techniques to optimize and enhance the code

using machine specific knowledge are desirable. The size of programs for PCs typically

extends into the megabytes for moderately complex programs. The size of simple

embedded systems programs may be as small as a thousand bytes or less. A medium

size embedded system might need 32K or 64K of code for relatively complex functions.

Some embedded systems use megabytes of storage for large tables, user text

messages or data logging.

FIGURE 1-7: A COMPILER CONVERTS SOURCE CODE INTO MACHINE

INSTRUCTIONS

int main (void)

{

counter = 1;

TRISB =0;

while (input1 = 0)

{

PORTB = count;

counter++;

}

COMPILER

01101111

10001000

11001101

10100001

00110011

01011101

00110001

11100101