Tuesday, December 22, 2009

Notes from the new world of video cable confusion and iMac target display mode

Once upon a time I had to know about hercules graphics cards and RGB cards and about half a dozen forgotten video standards from the dawn of the PC.

Mercifully we've more or less sorted out screen resolutions (albeit without our long promised resolution independence). Video cables though, not so much. DRM, mega-screens, and licensing struggles have blown through a half-dozen cable standards. Here's what I deal with in my own home with our new flickering 27" i5 iMac.
MacBook: Apple Mini DVI. I have adapters to VGA and DVI.
iBook: mini-VGA port, I have a mini-VGA to VGA adapter.
Dell 2007WFP (1680x1050) display: DVI and VGA
Ancient XP box: VGA
iMac G5: mini-VGA (amazingly, same as iBook)
iMac i5 27" as computer: mini-DisplayPort
iMac i5 27" as display (1560x1440): mini-DisplayPort
Dell Laptop (corporate): standard VGA and (full size) DisplayPort
Prior to the i5 I had the following adapter cables
  • mini-VGA to VGA
  • mini-VGA to DVI
  • mini-DVI to DVI
  • mini-DVI to VGA
Recently I've added these cables/adapters
They were both relatively inexpensive, even with shipping (which was reasonably priced in both cases). So far both of them work. I was surprised how useful using the i5 as an external display is.

Using the mini-DisplayPort to DVI (from eForcity via Amazon, $7) adapter I can connect the i5 to the lower-pixel density Dell 2007WFP. I use the Dell for easy-on-the-eyes reading and the i5 for photo, video and as a work space. It's not a bad combination.

Using the mini-DisplayPort to (male) DisplayPort 3 foot cable I can connect my Dell laptop and use the iMac as an external display (Target display mode). This is a wee bit tricky. When I first tried it my Dell blue screened, but after rebooting it was ok. This didn't surprise me, it's always been fragile about external displays. When it worked it drove the i5 at full resolution, which impressed me. The i5 went into target display mode when I plugged in the DisplayPort cable -- but it didn't return to normal mode when I pulled it. The almost-undocumented secret is to use Command+F2 to toggle display modes.

Some other tips about using the iMac as a really big monitor (from Apple, except mine didn't leave target mode when I pulled the cable ...) ...
  • Applications running on the 27-inch iMac computer remain open and running while it is in Target Display mode.
  • Use the keyboard of the 27-inch iMac to adjust display brightness and sound volume and to control media playback of applications running on the 27-inch iMac in Target Display mode. Other keyboard and mouse input is disabled on the 27-inch iMac while it is in Target Display mode.
  • The 27-inch iMac works like any other external display while it is in Target Display mode, except that you cannot access its built-in iSight or USB and FireWire ports. To change display settings, open System Preferences on the external source computer and choose Display from the View menu.
  • Mac OS X on the 27-inch iMac ignores some sleep requests while it is in Target Display mode, but forced sleep, restart, and shutdown commands will still work. If the external source goes into idle display sleep, the 27-inch iMac in Target Display mode will go dark until activity resumes on the external source.
  • If you shut down, sleep, or detach the external source while In Target Display mode, the 27-inch iMac will leave Target Display mode.
  • The Mini DisplayPort in the 27-inch iMac can receive only DisplayPort compliant video and audio signals. Converters not made by Apple may provide options to convert other electrical, video, and audio protocols to Mini DisplayPort compliant signals.
Incidentally, I can't use the MacBook to drive the i5 display, but I can use it with the smaller Dell display.

Phew. I hope things settle down to using mini-DisplayPort and/or DisplayPort for a while.
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Mitch said...

Gordon, Thanks for this post... I've been trying to find some information on how well this works and I think you've sent me down a good path.

I work at a major corp that allows me to work virtually and they give me a Dell D630 with Windows XP (yep, still in the dark ages). For several years now, I've used MS Remote Desktop to get into the machine from my iMac which works like a charm.

However, the company security guys have now gone crazy (IMHO) and are forcing us to stop using Remote Desktop because they're afraid of any non-corporate access to the equipment. Since I don't want to give up the 27" glorious monitor, I'm looking to drive the iMac with the Dell laptop and to use a KVM to stick with only one keyboard and mouse.

I'm hoping the KVM switch will cut off the signal to the iMac and take it out of target display mode. Do you think that will work correctly? It seems to me that from the videos I've seen, it is the live signal going thru the cable that triggers target display mode and I think I'll be ok.

I don't think it is going to be ideal, but at least your post has given me information and some hope. I don't really want to have 2 computers on my desk and 2 sets of monitors.

Anonymous said...

what other adaptors did you use to connect the dell laptop to the iMac 27".. You had a mini-DVI to mini-DVI.. What cable did your VGA male to mini-DVI ?


John Gordon said...

For the Dell to iMac connection I just use the mini-DisplayPort to DisplayPort cable mentioned in the post. This Dell has DisplayPort output.