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PEN Function Details
 
Syntax
  PEN(n)
 
The argument n indicates what value is to be returned. It is a numeric
expression in the range 0-9.
 
  Note: PEN function does not work when the mouse driver is enabled
        because the mouse driver uses the PEN function's BIOS calls.
        Use mouse function 14 to disable the driver's lightpen emulation.
        Mouse function 13 turns emulation back on. See your mouse manual
        for more information.
 
The following list describes the values for n and the corresponding
values returned by PEN:
 
  Argument   Value Returned
 
  0          The most recent pen use: -1 if pen was down since last
             poll, 0 if not
  1          The x pixel coordinate where pen was last pressed
  2          The y pixel coordinate where pen was last pressed
  3          The current pen-switch value: -1 if down, 0 if up
  4          The last known valid x pixel coordinate
  5          The last known valid y pixel coordinate
  6          The character row position where pen was last pressed
  7          The character column position where pen was last pressed
  8          The last known character row where the pen was positioned
  9          The last known character column where the pen was
             positioned