In a blog entry last month, I commented that neither I nor an Apple employee could get clamshell mode to work with a new MacBook Pro (MBP) connected to a new LED Cinema Display at the Apple Store. That is, once we closed the lid on the laptop, the Cinema Display turned off and would not turn back on.

Subsequently, I contacted Apple about this and they assured me that clamshell mode does work with the new hardware. So I hoofed it back to the Apple Store for a retest. Not sure what happened between the two trips, but this time clamshell mode indeed worked as promised! While at the Store, I took the opportunity to do some additional testing of different variations of putting the MacBook Pro to sleep and waking it up -- to see how each variation affected the MBP-Cinema Display combo. Here's what I found:

• If you close the lid on the MBP, both the MBP and the Cinema Display turn off. If you then press a key on the keyboard connected to the Cinema Display, the Display comes back on while the MacBook's display stays off. This is the classic clamshell mode.

What happens if you now open the lid of the MBP? The MBP's display does not come back on. The keyboard and trackpad on the MBP become active, but the screen does not light up. However, if you disconnect the Cinema Display from the MBP, the MBP's screen returns. And, as expected, if you reconnect the Cinema Display, you now have both screens working again.

• If you select Sleep from the Apple menu, both screens turn off as the MBP goes to sleep. No surprise here. If you now press a key on either keyboard (the MacBook's keyboard or the one connected to the Cinema Display), both screens come back on.

Similarly, if you initially close the lid to put the MBP to sleep and then lift the lid (before pressing any keys on the keyboard connected to the Cinema Display), both displays light back up.

• So...here's my recommended procedure to put a MBP into clamshell mode and then get both screens active again...without having to disconnect/reconnect the display:

1. Close the lid on the MBP.
2. Press a key on the keyboard connected to the Cinema Display to activate clamshell mode.
3. When you want to have both screen's active again, select Sleep from the Apple menu. This turns off the Cinema Display as it puts the MBP to sleep. Now, lift the lid of the MBP. Both displays should come back on without any further hassle.

[Update: Posted November 30] As pointed out by reader John Herring, a wireless keyboard and mouse attached to the Cinema Display may not work at all after closing the lid on the MBP.