program delta ;

(*** VGA 80*25 mode assumed ***)

procedure CharGenModeOn ;
begin
  asm
      cli
      mov       dx,03C4h
      mov       ax,0100h
      out       dx,ax
      mov       ax,0402h
      out       dx,ax
      mov       ax,0704h
      out       dx,ax
      mov       ax,0300h
      out       dx,ax
      sti
      mov       dl,0CEh
      mov       ax,0204h
      out       dx,ax
      mov       ax,0005h
      out       dx,ax
      mov       ax,0006h
      out       dx,ax
      end ;
  end ;

procedure CharGenModeOff ;
begin
  asm
      cli
      mov       dx,03C4h
      mov       ax,0100h
      out       dx,ax
      mov       ax,0302h
      out       dx,ax
      mov       ax,0304h
      out       dx,ax
      mov       ax,0300h
      out       dx,ax
      sti
      mov       dl,0CEh
      mov       ax,0004h
      out       dx,ax
      mov       ax,1005h
      out       dx,ax
      mov       ax,0E06h
      out       dx,ax
      mov       ah,0Fh
      int       10h
      cmp       al,7
      jne       @skip
      mov       ax,0806h
      out       dx,ax
      @skip:
      end ;
  end ;

var J : integer ;

const CS : array [0..15] of char =
  #$00#$00#$18#$18#$18#$2C#$2C#$2C#$46#$46#$46#$FF#$00#$00#$00#$00 ;

BEGIN ; Writeln('www.merlyn.demon.co.uk') ;
CharGenModeOn  { Get access to character map } ;
{ Characters are stored in a 8x32 pixel matrix, allowing for characters
  that are 32 scan lines high.  Each byte in the buffer represents one
  scan line of a single character.  In the 80x25 character mode only the
  first 16 scan lines are displayed, so we need to be a little careful
  about what bytes are changed. }
for J := 0 to 15 do { Top 16 scan lines OF  }
  Mem[SegA000:32*Ord('')+J] := byte(CS[J]) ;
CharGenModeOff { Restore normal video operations } ;
END.