bas7advr.hlp (Topic list)
PEN Function Details
  Syntax  Details  Example                 Contents  Index  Back
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PEN returns lightpen status. Ten types of status can be returned,
depending on the argument you use.
 
PEN(n%)
 
Usage Note
    ■ The 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.