program GrafAsm;

 uses crt;

var   pantalla: array [0..319,0..199]  of byte absolute $A000:$0000;         { Pues la pantalla  }
      bucle: integer;
const NumPuntos = 10000;       { Número de puntos que dibujaremos }

 procedure Modo320; assembler;
 {$ASMMODE intel}
 asm
   mov eax,$13
   int $10
 end;

 procedure ModoTxt; assembler;
  {$ASMMODE intel}
 asm
   mov eax,3
   int $10
 end;

 begin
 Modo320;
   for bucle := 1 to NumPuntos do 
     Pantalla[ random(319), random(199)] := random(255) ; 
   readln;
ModoTxt;
 end.
    

Iirc, FreePascal only compiles for 32- and 64-bit - you're trying to use 16-bit addressing as well as BIOS calls... so this isn't going to work

We can help you, but what actually you want to do? IMHO, the above program is easier to be written directly in FASM. (In this case you can create it for 16 bit dos and these interrupts will work)

var pantalla: array [0..319,0..199]of byte absolute $A0000;    

Try linear address

Code:

var pantalla: array [0..319,0..199]of byte absolute $A0000;    

:~/Escritorio/binario$ fpc vga3.pas
Free Pascal Compiler version 2.4.0-2 [2010/03/06] for i386
Copyright (c) 1993-2009 by Florian Klaempfl
Target OS: Linux for i386
Compiling vga3.pas
Linking vga3
/usr/bin/ld: warning: link.res contains output sections; did you forget -T?
46 lines compiled, 0.1 sec

:~/Escritorio/binario$ ./vga3
Runtime error 216 at $080480A5
$080480A5
$08069A47