procedure Sound(Freq: Word);
var
 B: Byte;
begin
 if Freq > 18 then
 begin
 Freq := Word(1193181 div LongInt(Freq));
 B := Byte(GetPort($61));

 if (B and 3) = 0 then
 begin
 SetPort($61, Word(B or 3));
 SetPort($43, $B6);
 end;

 SetPort($42, Freq);
 SetPort($42, Freq shr 8);
 end;
end;

procedure NoSound;
var
 Value: Word;
begin
 Value := GetPort($61) and $FC;
 SetPort($61, Value);
end;

procedure SetPort(address, Value: Word);
var
 bValue: byte;
begin
 bValue := trunc(Value and 255);
 asm
 mov dx, address
 mov al, bValue
 out dx, al
 end;
end;

function GetPort(address: word): word;
var
 bValue: byte;
begin
 asm
 mov dx, address
 in al, dx
 mov bValue, al
 end;
 GetPort := bValue;
end;