http://developer.apple.com/legacy/mac/library/documentation/Hardware/Developer_Notes/Macintosh_CPUs-G4/iMac_Sep03/03_Input-Output/q26bc_inout.html#//apple_ref/doc/uid/TP40000875-CH207-DontLinkElementID_14
Video Monitor Port
The iMac computer has a port for an external video monitor and supports video
mirroring mode. Video mirroring mode displays the same information on both
monitors, enabling the control of a presentation on one display, while allowing
an audience to watch the presentation on a second display or projector.
Due to display mirroring, the external monitor could have black borders during
mirroring, depending on the supported timings between the two displays and on
the monitor=E2=80=99s selection algotithm. Both displays show full-sized images
only
when the display resolution for the second monitor is set to the first
display=E2=80=99s native resolution: 1440x900 on the 17-inch display and
1024x768 on
the 15-inch display.
The external monitor supports user-selectable display sizes up to 1600x1200 at
75 Hz.
Monitor Connector
The video display connector is a 14-pin rectangular connector, Hosiden TCX3143,
or compatible. The connector accepts either a VGA adapter or a composite
adapter. The system requires a composite adapter to use composite output over
this connector. The connector pins are identified in Table 3-3.
Figure 3-3 Video display connector
Video display connector
The pins and signals are listed in Table 3-8. An adapter is available for use
with monitors with VGA 15-pin miniature D-type connectors.
Table 3-8 Video signals for a VGA R-G-B display
Pin Signal name
1 Ground
2 VSync
3 Hsync
4 Red return
5 Red video
6 Green return
7 Green video
8 +5 volts
9 Blue video
10 DDC data
11 DDC clock
12 Ground
13 /Cable detect
14 Blue return
The cable detect function on pin 13 is implemented by connecting pin 13 to
ground in the display cable. The computer gathers the display's capabilities
by
reading its EDID (Extended Display Identification Data) via DDC.
The video display connector is compliant with the VESA specification.
Video Display Adapter
The iMac computer detects the type of display adapter that is plugged in and
programs the graphics IC to route the appropriate video signals to the
connector. The signal assignments on the video connector when the composite
adapter is attached are shown in Table 3-9.
Table 3-9 Video signals for a TV display
Pin Signal name
1 Ground
2 n.c.
3 n.c.
4 Ground
5 S-video C
6 Ground
7 S-video Y
8 +5 volts
9 Composite video
10 DDC data
11 DDC clock
12 Ground
13 Ground (for /Cable Detect)
14 Ground
Composite video and S-video signals can be displayed on either an NTSC display
or a PAL display. When a display is connected by way of the composite adapter,
the computer detects this configuration and enables the composite and S-video
outputs. The settings for the resolutions and standards (NTSC or PAL) are then
selectable in System Preferences.
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