The Apple IIGS has two video ports: an RCA phono jack and a 15-pin D-Type
connector. An EIA-standard composite video signal (2.0V white, 0.75V black,
0.0V sync., 75-ohm impedance) is available from both connectors. This
composite signal drives many monitors such as the AppleColor Composite
Monitor, the Apple Monochrome Monitor, and a TV unit with an RF modulator.
While composite video monitors can be used with the Apple IIGS, they don't
fully render the 320 x 200- and 640 x 200-pixel color graphics potential of
the new system.
The 15-pin connector analog RGB signals provide full color graphics display
capability. Note that the Apple IIGS outputs analog, not digital, RGB
signals. The designers preferred the unrestricted character of an analog
signal for the ability of the Apple IIGS to support 4096 colors. Apple offers
a new platinum Apple Color RGB Monitor for the Apple IIGS. Other analog RGB
monitors known to work with the Apple IIGS include several models by Hitachi,
Panasonic, Sanyo, Mitsubishi, Conrac, and Commodore.
To check if your monitor is analog RGB, consult the manual. Check the pinouts
before connecting the monitor to an Apple IIGS to make sure your monitor is
compatible with pins 7 and 8. The Apple IIGS's 15-pin RGB video signals are
as follows:
Pin Signal
1 Signal ground (Red)
2 Analog RED with sync
3 Composite sync
4 No connection
5 Analog GREEN with sync
6 Signal ground (Green)
7 -5 volts DC
8 +12 volts DC
9 Analog BLUE with sync
10 No connection
11 Sound 1V peak-to-peak
12 NTSC/composite color video out
13 Signal ground (Blue)
14 No connection
15 No connection
Shield System ground
There's no simple, straightforward way to invert sync or to separate
horizontal and vertical sync on the composite signal for incompatible
monitors, but it could be done as an interface product.
Some types and makes of monitors won't work at all. Digital RGB monitors
either won't work at all or will work with unpredictable results. Digital RGB
monitors with these problems are Apple's older Color Monitor 100 and IBM RGB
monitors (IBM's RGB monitors need inverted sync in addition to TTL video
signals.). Apple's Flat Panel Display has incompatible signals.
Do NOT assume that a DB-15 connector on your color monitor means it's analog
RGB.