User`s guide

For other sources, see the Vendors listing in Csa21MAIN2 or on the web page
at http://home.swbell.net/rubywand/A2FAQs3VENDORS.html .
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From: David Empson
024- What kind of RGB monitors will work with a IIc and a
Laser 128?
I don't know about the Laser. The IIc doesn't have built-in RGB output. Its
video port provides several low-level timing signals which allow RGB data to be
decoded from the composite video signal (which is also provided on the port),
but this requires external hardware.
The "standard" IIc RGB adapter (assuming there was one) would probably have
produced digital RGB output, the same as the Apple III and the Apple IIe memory
expansion cards with RGB output. With a digital RGB monitor, standard digital
logic levels (TTL) indicate whether a colour (or colour weighting) is present or
absent. One wire is required for each bit of each primary colour.
The IIgs, on the other hand, produces an analog RGB signal - a voltage on the
Red, Green and Blue outputs represents the intensity of each primary colour. Any
number of shades of each colour can be supported, by providing a finer
resolution digital to analog converter within the computer. The IIgs has 4-bit
D-to-A for each primary colour. High-end video cards on the Mac and PC (SVGA)
use 8-bit D-to-A for each primary colour.
Digital RGB monitors cannot be used with an Analog RGB signal (unless
comparators are used to generate a digital signal from the analog one).
Analog RGB monitors cannot normally be used with a Digital RGB signal, but
generating an analog signal is possible with a resistor network (an example of
this is given in the Apple III Owner's Guide). In some cases, it may be
possible to plug an Analog RGB monitor into a Digital RGB output, but it won't
produce the correct colours (when compared with a Digital RGB monitor).
There are two common types of digital RGB monitor: one type will work with the
Apple III, Apple IIe (with RGB card), Apple IIc (with RGB adapter) and CGA on an
IBM PC (different cables or adapters are required). This type has intensity and
one bit each for red, green and blue (16 colours in total).
The second type is usable with EGA. This has two bits each for red, green and
blue (64 colours in total). These monitors also have a higher scan frequency
than the first type, and cannot be used with an Apple II (unless a card has been
specially designed to use them).
Analog RGB monitors are mainly classified by the scan frequency and resolution.
The IIgs RGB monitor (A2M6014X) operates at similar frequencies to television -
around 15 kHz. Macintosh and VGA/SVGA RGB monitors do not support such low scan
rates, and typically work at about 30 kHz or higher. The Mac cannot use the
IIgs RGB monitor, and the IIgs cannot use Mac/VGA RGB monitors.