unit usebios;
{allows use of clrscr and gotoXY without messing up file redirection}
{Author: Lin Jensen,
 Date  : October 6, 1996
}
interface
const       {your program can CHANGE these global variables}
   TextAttr : byte = $07;  {black with white chars, used by ClrScr }
   PromptAttr : byte = $0E;  {black with yellow chars - for PROMPTs}
   PressAttr : byte = $CE;  {red with blinking yellow chars,
                             for Press a Key message}

procedure ClrScr;    { clears the screen, stores page # and screen width}
procedure gotoXY (x,y:integer);
procedure WaitKeyPress;        {writes "Press a key" and waits until }
procedure Prompt (please:string);  {write a 'prompt' suitable for user input,
                                   stays to screen even if output redirected,
                                   otherwise same as WRITE(please) }

IMPLEMENTATION
type
   char11 = array [0..10] of char;
var
   screen_page : byte;
   screen_width: byte;
const
   press : char11 = 'Press a key';
   blank : char11 = '           ';

procedure gotoXY (x,y:integer);
begin
ASM
{GOTORC  proc        ;position cursor according to DH, DL}
        DEC     X       {Pascal from 1, bios from 0}
        DEC     Y
        MOV     AH, $02        { ;BIOS service "position cursor"}
        MOV     BH, screen_page        {   ;page 0 or as set by clearscreen}
        MOV     DH, BYTE PTR Y    { ;row and column are passed by caller     }
        MOV     DL, BYTE PTR X
        INT     $10             {;call BIOS video services}
END;  {asm}
end;{gotoRC  endp}

procedure clrScr;    { proc    ;clear screen, store page and segment address}
label done;
begin
{;Test video mode, change pageseg for colour if necessary}
ASM
        MOV     AH, $0F        { ;read video mode }
        INT     $10            { ;Call BIOS       }
        mov     Screen_page, bh { information enabling us to write directly}
        mov     Screen_width,ah {   ; to video memory}
        CMP     AL,7            {AL is mode, is it monochrome?}
           JA    DONE           {probably graphics, do nothing }

        MOV     AX, $0600     { CLEAR SCREEN function, all lines}
        MOV     BH,TextAttr {black bkgd, white chars unless changed}
        MOV     CX, 0     {;upper left     }
        MOV     DH,24     {;assume 25 lines }
        MOV     DL,screen_width
        dec     dl
        INT     $10     { call BIOS video services}
end; {asm}
{; position cursor at upper left}
        GotoXY(1,1);
done:
END; {clearScreen     endp}

procedure WaitKeyPress;        {writes "Press a key" and waits until }
begin
asm
        mov ah,03h      {read cursor position}
        mov bh, screen_page
        int 10h
        mov ah, $13     {bios write string}
        mov al, $00     {dont move cursor}
        mov bl, PressAttr     {blinking yellow on red}
        mov cx, 11      {length of string}
        push bp         {es:bp holds full address of string}
        mov bp, ds
        mov es, bp
        mov bp, offset press
        int 10h
{-------------------- wait for key _______}
        mov ah, $00
        int $16
{ -------------------- blank out message -}
        mov ah, $13     {bios write string}
        mov al, $00     {dont move cursor}
        mov bl, TextAttr {attribute back to normal}
        mov bp, offset blank
        int $10
        pop bp
end;
end;

procedure Prompt (please:string);
                 {write a 'prompt' suitable for user input,
                 stays to screen even if output redirected,
                 otherwise same as WRITE(please) }
begin
asm
        mov ah,03h      {read cursor position - to DX}
        mov bh, screen_page
        int 10h
   les   si, [bp+6]       {address of please from stack}
   mov   cl, es:[si]      {length byte}
   mov   ch, 0            {pad cx}
   inc   si               {first char of string}
        mov ah, $13     {bios write string}
        mov al, $01     {do move cursor}
        mov bl, PromptAttr     {yellow on black}
        push bp         {es:bp holds full address of string}
        mov bp, si
        int 10h
        pop bp
end;
end; {prompt}
begin
   screen_page := 0;    {default page no. until ClrScr called}
end.