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Pointer constants

 
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Diego López



Joined: 25 May 2012
Posts: 11
Location: Colombia

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Pointer constants
PostPosted: Wed Dec 05, 2012 11:43 am     Reply with quote
Hi, sorry I do not speak English, I speak Spanish.

I call collaboration.

I work pointers to constants in this program, can you help?

Thank you very much.
Code:

#include <16f876A.h>

#use delay(clock=4mhz)
#fuses xt,put,brownout,nowdt

#byte   porta=5      //Definicion de variables del pic
#byte   portb=6
#byte   portc=7

#define   port_lcd portb

int status;

char rom *dir_tabla_g;
char rom tab_grafico1[] = {   0xff,0xff,
                     0xff,0xff,
                     0xc0,0x0f,
                     0xc0,0x0f,
                     0xc0,0x0f,
                     0xcf,0xcf,
                     0xcc,0xcf,
                     0xfc,0xff,
                     0xfc,0xff,
                     0xfc,0xc3,
                     0xfc,0xc3,
                     0x84,0xdb,
                     0x84,0xdb,
                     0xfc,0xc3,
                     0xfc,0xc3,
                     0xfc,0xff};

void grafico(int y, x, filas, columnas);

///////////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////////
#zero_ram   //Borrado de la memoria ram

void main()      //Rutina principal
{
set_tris_a(0b000000);      //Configuracion de entradas y salidas del puerto A
set_tris_b(0b00000000);      //Configuracion de entradas y salidas del puerto B
//port_b_pullups(true);      //Habilitación de las resistencias pull-ups
porta = 0xff;
portb = 0;
///////////////////////////////////////////////////////////////////////////////
//se carga el puntero de la tabla a presentar
dir_tabla_g = &tab_grafico1[0];

//y,x,filas,columnas
grafico(1,1,16,2);
///////////////////////////////////////////////////////////////////////////////
while(true)      //Rutina general
   {
   
   }
}
///////////////////////////////////////////////////////////////////////////////
//realiza un barrido de filas y columnas copiando la tabla de constantes
void grafico(int y, x, filas, columnas)
{
   int i1, i2;
   int registro = 0;
   
   for(i1=0;i1<filas;i1++)
   {
      
      for(i2=0;i2<columnas;i2++)
      {
         status = *dir_tabla_g + registro;
         registro++;
      }
   }
}   
///////////////////////////////////////////////////////////////////////////////
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Thu Dec 06, 2012 1:01 am     Reply with quote
I made the changes shown in the grafico() function shown below.
Then it worked. With those changes, I ran your program in MPLAB
simulator and I got the following output. It matches your tab_grafico1[]
table. I tested the program with CCS version 4.140:
Code:

ff ff
ff ff
c0 0f
c0 0f
c0 0f
cf cf
cc cf
fc ff
fc ff
fc c3
fc c3
84 db
84 db
fc c3
fc c3
fc ff


This is the grafico() function with changes noted in comments:
Code:

void grafico(int y, x, filas, columnas)
{
   int i1, i2;
   int registro = 0;
   
   for(i1=0;i1<filas;i1++)
   {
      for(i2=0;i2<columnas;i2++)
      {
       dir_tabla_g = tab_grafico1;  // *** Added this line
       dir_tabla_g += registro;     // *** Added this line

       status = *dir_tabla_g;       // *** Modified this line
         
       printf("%x ", status);       // *** Added for debug output
       registro++;
      }
    printf("\r");                   // *** Added for debug output
   }
 printf("\r");                      // *** Added for debug output
}   



Note that this line in your original program is wrong:
Quote:
status = *dir_tabla_g + registro;

You are doing pointer arithmetic incorrectly. But even if you do it
write the line correctly as shown below, the program still doesn't work:
Code:
 status = *(dir_tabla_g + registro);

To make the program work correctly, you have to do it the way
that I show in the modified grafico() function given above.

The problem occurs because if you try to do pointer arithmetic (even as
shown above), the compiler does not call the @READ_PROGRAM_MEMORY
library routine. But if you use the modified grafico() function, then it
does call the library code. Then it works.
Diego López



Joined: 25 May 2012
Posts: 11
Location: Colombia

View user's profile Send private message

PostPosted: Thu Dec 06, 2012 8:09 am     Reply with quote
Hello friend, thank you very much for answering.

This works perfect

Code:
for(i2=0;i2<columnas;i2++)
      {
         status = *(dir_tabla_g + registro);
         registro++;
      }


thank you
Diego López



Joined: 25 May 2012
Posts: 11
Location: Colombia

View user's profile Send private message

PostPosted: Tue Dec 11, 2012 9:50 am     Reply with quote
Hello friends,

The constant pointer i work well in this way,

Code:
int variable;

char rom *dir_tabla;

char rom c_30[] = {0x3c,0x42,0x42,0x42,0x42,0x42,0x42,0x42,0x3c,0x00,0x00,0x00,};
char rom c_31[] = {0x08,0x38,0x08,0x08,0x08,0x08,0x08,0x08,0x7f,0x00,0x00,0x00,};
char rom c_32[] = {0x3c,0x42,0x42,0x04,0x08,0x10,0x20,0x42,0x7e,0x00,0x00,0x00,};
char rom c_33[] = {0x3c,0x42,0x02,0x02,0x0c,0x02,0x02,0x42,0x3c,0x00,0x00,0x00,};
char rom c_34[] = {0x0c,0x14,0x14,0x24,0x24,0x7e,0x04,0x04,0x1e,0x00,0x00,0x00,};
char rom c_35[] = {0x3e,0x20,0x20,0x3c,0x02,0x02,0x02,0x42,0x3c,0x00,0x00,0x00,};


dir_tabla = c_30;
grafico1();

void grafico1()
{
   int registro;
   
   for(registro = 0; registro<12;registro++)
   {
      variable = *(dir_tabla + registro);
   }
}



can teach me how to make a tables pointer?

thank you very much

! I speak Spanish!
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