The video output port supports 8-bit video output (512 KB of non-expandable VRAM) for 256 colors on Apple 12-inch, 13-inch, and 16-inch RGB monitors; and 4-bit video with 16 shades of gray on the Apple Portrait Display. VGA and SVGA modes are supported with appropriate adapter cables. The video controller emulates a NuBus card in slot $E, so the video output system appears to software as a standard video card.
An adapter cable included with the computer allows users to attach a standard Apple video cable. The external video interface is enabled by attaching a monitor and restarting the computer. To connect a VGA monitor to the Macintosh video port, an adapter cable is required. Third-party cable vendors should have these cables available for purchase.
During the boot process, ROM code tests the monitor sense lines and activates the video output system if a recognized monitor is attached. If no monitor is found, the video output system is deactivated to conserve power. Because the video output circuitry consumes additional power, Apple recommends that customers use the AC adapter when using an external monitor.
* Video Scan Rates:
Monitor Resolution Dot clock
. Width (pixels) Height (pixels) Depth (bits) (MHz)
12-inch RGB 512 384 8 15.6672
13-inch RGB 640 480 8 30.2400
VGA 640 480 8 25.1750
SVGA 800 600 8 36.000
Portrait 640 870 4 57.2832
16-inch RGB 832 624 8 57.2832
The AudioVision 14 Display is also compatible.
In normal operation the video output circuitry acts like a second monitor to extend the user's desktop. Alternatively, the user can select video mirroring mode, in which the external monitor mirrors the internal LCD. In mirror mode, software blanks the edges of the larger screen to match the horizontal and vertical pixel resolution of the smaller screen.
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