Int 66 Fn 41  - Pendos - Pkeyus - Set ???                                  [n]

   AH = 41h
   BX = ???
   CL = ??? (08h-20h)
   DL = screen column??? (<= 50h)
   DH = screen row???  (<= 3Ch)

Return: AX = status (0000h successful, 0001h error)

Note:  this function also sets an internal flag

See Also: AH=42h,AH=43h