procedure chxtin(asc:packed array [lo..hi:integer] of char;
		 var bin:integer;
                 var pos:integer); external;
{
 Convert an ascii string of hex digits to an integer. Will start converting
 at pos and will do upto 4 digits. Will stop if end of string is encountered
 or none hex digit is encountered.  Pos will be left at the next position
 to convert.
}