Recently i was working with 8-bit pic16f877 microcontroller and i want to place program code at a specific rom(read only memory) location. I was working with xc8 compiler and mplabx ide. Previously i did this same thing many times while using c18 c compiler. C18 compiler uses #pragma code directives to accomplish this task. But when i started with xc8 compiler and put the same #pragma code directive in my code the compiler starts giving errors. I found that the xc8 didn’t support #pragma code directives. So now i have to locate the xc8 macros for accomplishing this task. I searched the internet but did not found any major help regarding it. Then i decided to read the xc8 compiler datasheet. After lot of reading i found some valuable information and now i want to share it with the microcontroller projects community.
I found three methods to store data at a particular location in program memory of pic microcontroller, when working with xc8 compiler. The three macros/directives that i found were
- __section()
- __at()
- ‘@’ qualifier
The first two methods are little complex and difficult to manage, while the third one the ‘@’ qualifier is easy to manage and use. Before using the ‘@’ qualifier one should first check the program memory banks addresses range of the pic microcontroller that he is using. I am using pic16f877 microcontroller, its program memory address range is from 0x0000 to 0x1FFF. The word size is 14 bits and memory size is 8 KB.
I want my code to start at program memory location/address 0x200. To do so i placed the ‘@’ qualifier at the end of the main function. See the above main function initialization. At the end of the closing brackets i placed the @ qualifier with the program memory address where i want my code to be placed in flash/rom. In the main function i have two for loop functions, generating a random delay.
int main(int argc, char** argv) @ 0x200 {}
/*
* File: code.c
* Author: Usman Ali Butt
* Property off: www.microcontroller-project.com
* Created on 15 March, 2017, 3:38 PM
*/
// PIC16F877 Configuration Bit Settings
// ‘C’ source line config statements
#include <xc.h>
// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
// CONFIGURATION bits of pic16f877 microcontroller
#pragma config FOSC = EXTRC // Oscillator Selection bits (RC oscillator)
#pragma config WDTE = OFF // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config CP = OFF // FLASH Program Memory Code Protection bits (Code protection off)
#pragma config BOREN = ON // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = ON // Low Voltage In-Circuit Serial Programming Enable bit
#pragma config CPD = OFF // Data EE Memory Code Protection (Code Protection off)
// FLASH Program Memory Write Enable (Unprotected program memory may be written to by EECON control)
#pragma config WRT = ON
#include <stdio.h>
#include <stdlib.h>
#include <pic16f877.h>
int main(int argc, char** argv) @ 0x200 {//Program memory Address specified
for(int i=0;i<1000;i++){
for(int j=0;j<10000;j++);
}
return (EXIT_SUCCESS);
}
void main() @ 0x100 {}