Guidance: Shifting between Mirroring and Split Screen Modes
Troubleshooting: Computer Screen Doesn't Show Cursor
When a laptop is connected to a computer projector or other display device,
Mac OS X allows the user either to
- display the same screen on both displays (mirroring), or
- split the screen between between the two displays (screen splitting).
Sometimes a CartMac user will shift from mirroring mode to split screen mode
and leave it that way with the projector turned off. Symptoms might include:
- the laptop display has shrunk laterally, leaving black margins on each side
of it; and/or
- the cursor doesn't appear anywhere on the laptop display; and/or
- the laptop's display doesn't show what the projector does on the screen.
These symptoms can disconcert the next user, who might not realize that the
screen is in split mode and can't find the cursor (because it resides on the
(possibly now-dark) projected screen rather than the laptop display. (See below
for instructions for restoring normal mirroring
To understanding how to resolve this dilemma, it helps first to understand
how to shift from the normal mirroring mode into split screen mode.
Toggling from mirroring mode to split screen mode:
First, the easy way. There should be a "display" icon somewhere along
the right side of the CartMac's toolbar along the top edge of the laptop display.
If it's there, click on it to get a menu and select "Turn on mirroring".
That should do the trick.(You can than select "Turn off mirroring"
to toggle back to split screen mode.)
Second, the hard way, which you must do if there is no display icon in the
- Open System Preferences (pull down the Apple menu [upper-left corner of
the screen] and select "System Preferences").
- Select "Displays". This produces two dialog boxes, one entitled
"Color LCD" and beneath it another entitled "Epson PJ"
(referring to the second display device, the Epson projector) or whatever
your projector is.
- On the Epson PJ dialog box, click on the "Arrangement" button
near the top of the box. This should produce a cartoon representation of two
screen displays, one on top of the other.
- Uncheck the "Mirror displays" checkbox in the lower left-hand
corner. The screen should flicker blue-blank and then generate two separate
screens, one on the laptop and the other projected. Note the following:
- The cursor resides on the projected screen, along with
the dock and the Epson PJ dialog box. The Epson PJ dialog box shows
a cartoon representation of two screen displays side by side. (Its "Mirror
displays" check button (lower left-hand cornder) is unchecked.)
- The CartMac hard drive icon and screen-top menu bar reside on the
laptop screen. So does the Color LCD dialog box.
- You can slide the cursor leftward from the projected screen onto the
laptop screen and back again. Applications started from the dock (on
the projected screen) will open on the laptop screen, but you can drag the
open windows rightward onto the projected screen and back again.
In split-screen mode, the computer behaves as follows:
- The display dimensions reported by the computer change. If the laptop display
dimensions are set to 1920x1080 (the highest resolution for CartMacs) when
in mirroring mode, then toggling to split screen changes the dimensions to
become 1440x900 on the laptop and 1024x768 on the projected screen (using
the Epson projector in TH 604). Toggling back to mirroring mode changes the
resolution to 1024x768 (stretched) on the laptop and 1024x768 on the projected
(Both the Color LCD dialog box and the Epson PJ dialog box have a "Display"
button. Clicking on this button allows the user to change the dimensions and
resolution of the respective displays.)
- The screen acts as a single, extra-wide screen. The cursor can be moved
left and right between the two screen displays, and applications can be dragged
back and forth continuously between them, and even overlap between them.The
dock resides on projected screen, while screen-top menu items and the CartMac
hard drive icon reside on the laptop screen.
Shifting from split-screen mode to mirroring
To return to the normal, mirroring mode:
- If the projector is not hooked up to the CartMac and/or not turned on, hook
it up and/or turn it on, so you can see the projected screen.
- Locate the cursor (which probably resides on the projected screen. Also
locate the Epson PJ dialog box (which also probably resides on the projected
If you can't locate the Epson PJ dialog box, slide the cursor leftward onto
the laptop screen, pull down the Apple menu, select "System Preferences",
and select "Displays". The Epson PJ dialog box should appear on
one of the two screens.
- Click on the "Mirror displays" check button on the lower-left
corner of the Epson PJ dialog box. (This should produce the transient blue-blank
flicker, the Epson PJ dialog box will appear on top of the Color LCD dialog
box, the projected screen will show the same thing as the laptop screen.)
If you see no "Mirror displays" check button, then click on the
"Arrangement" button nera the top of the Epson PJ dialog box. You
should then see the button.
- The laptop screen is probably shrunken laterally and is flanked by black
bars. To return the laptop screen to normal resulution, refer again to the
Epson PJ dialog box. Click on the "Display" button near the top
of the box, then select "1280x1014" from the "Resolutions"
- Quit Systems Preferences.
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Page last modified 9/14/06 by Dave Dempsey.