;*****************************************************
; Listing 1 -- PC-controlled light dimmer
; "PC controls light dimmer," EDN,
; August 19, 1999, pg 140
;*****************************************************


Program         proj1;
uses            CRT,Strings;

procedure writedata(dword : longint);
var
 wraddr,readdr,strbaddr    : word;
 pPrintPort                        : ^word;
 rdta,ibte,bit,n                   : byte;
 to20,to28,num,data          : longint;

begin
pPrintPort := Ptr($40,$08);
wraddr := pPrintPort^;
to20:=$100000;
to28:=$10000000;
num:=to20*$40 + dword;
writeln('data= ',num);
PORT[wraddr]:=$97; {initialize to cs=0, sclk=0, sdin=1}
for n:= 1 to 32 do
begin
       ibte:=PORT[wraddr];
       PORT[wraddr]:= ibte OR 64; {set sclk=1}
       num:=num*2;
       bit:=0;
       if num >= to28 then
       begin
          bit:=1;
          num:=num-to28;
       end;
       ibte:=PORT[wraddr];
       if bit = 0 then PORT[wraddr]:= ibte AND 239 {set sdin=0}
       else PORT[wraddr]:= ibte OR 16;   {set sdin=1}
       ibte:=PORT[wraddr];
       PORT[wraddr]:= ibte AND 191;    {set sclk=0}
end;
end;

{***********************main********************}

var
inpkey : char;
num,num1    : longint;
label start;
begin

num := 0; 
start: inpkey := readkey;
if inpkey = 'q' then
   begin
   	if   (num+$1000)>$7fff0 then num:=$7fff0
else num:=num+$1000;
   end;
if inpkey = 'w' then
   begin
   	if (num-$1000)<-$7fff0 then num:=-$7fff0
   	else num:=num-$1000;
   end;
if inpkey = 'x' then exit;
if num<0 then num1:=$fffff+num
else num1:=num;
writedata(num1);
goto start
end.