New csa2 FAQs: F002MONITOR (Part 2 of 2)

[Rubywand <rubywand@swbell.net>]

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 adaptor (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
adaptor) and CGA on an IBM PC (different cables or adaptors 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.

Some third-party multisync monitors will work on the Mac/VGA and IIgs,
but these are very rare now.  Most multisyncs do not go as low as 15
kHz.

"15 kHz" and "30 kHz" refers to the horizontal scan frequency - Apple II
video output has a horizontal retrace roughly 15,000 times per second.

Vertical retrace is a different issue (it is much slower - usually 50 to
100 retraces per second), and most monitors are very flexible in the
supported vertical retrace rate, as far as I know.

This is also where "interlacing" comes in.  Interlacing is a technique
which doubles the effective vertical resolution of the monitor, by
performing two vertical scans (fields) per frame, with a slight vertical
shift in the second field.  The scan lines for the second field are
interleaved between the scan lines for the first field.

An interlaced display has more noticeable flicker than a non-interlaced
display with double the frame rate, because the phosphor is only lit
half as often.

For example, the Second Sight card will support a 400 line interlaced
mode with the IIgs RGB monitor.  There will probably be noticeable
flicker in this mode (especially out of the corner of your eye).

This mode will have 60 fields (i.e. 30 frames) per second, whereas the
standard IIgs video output is non-interlaced with 60 frames per second
(but only 200 lines vertical resolution).

(I'm assuming 60 Hz mode - the IIgs also support 50 Hz mode, for use in
countries with 50 Hz mains supplies and TVs.)

Television also uses interlacing - with NTSC, there are 525 lines per
interlaced frame and 30 frames per second, with alternating lines being
scanned on each pass of the electron beam (262.5 lines per field, 60
fields per second).

PAL uses 625 lines per frame, usually at 50 frames per second (312.5
lines per field, 25 fields per second).

______________________________


From: Rubywand

025- Can I replace my GS RGB monitor with one from a PC?

     Modern PC monitors have a Horizontal scan rate which is too high to
be compatible with the GS. Some users report success using some old PC
VGA monitors with a special adapter cable.

------------------------------


026- What are the specs and pin-out for the GS RGB monitor?

Max Resolution:   640 Horizontal dots x 200 Vertical dots
                 (200 lines of 640 dots)

Dot Pitch:        .37mm

CRT Size:          12"/  11.5" viewable

Video Bandwidth:   6.5MHz   (+/- 1.5DB)


Scanning Frequencies

               60Hz model            50Hz model

Horizontal:    15.734kHz             15.696kHz
Vertical:         60Hz                  50Hz


 Pin    Function

  1     Red video ground
  2     Red composite video
  3     Composite sync
  4    (not used)
  5     Green composite video
  6     Green video ground
  7    (not used)
  8    (not used)
  9     Blue composite video
 10    (not used)
 11    (not used)
 12    (not used)
 13     Blue video ground
 14    (not used)
 15    (not used)
Shell   Shield ground


----------------------------


027- Do I need to connect a monochrome monitor to my IIe to get
     readable 80-column text?

     Maybe not. Try turning down the "Color" control to get a B/W
display and adjusting Brightness and Contrast. This will, possibly, make
80-column text readable on your composite color monitor. Just how
readable will depend upon the particular monitor. On the popular Amdek
Color-1, readability is marginal at best. According to some user
reports, readability is decent on Apple's composite color monitor.


______________________________


From: Jim Krych (ab453@cleveland.Freenet.Edu)

028- Is there a high-quality replacement for RGB monitors?

     Yes. It's called the "VideoTurtle." (What follows comes from a
Video Turtle advertisement.)

     The VideoTurtle is a product that converts your RGB signal, known
as TV RGB-15.75KHz scan rate for NTSC, into S-Video!  S-Video is an
enhanced form of TV with better clarity and resolution than the "TV" we
are all familiar with.

     With your computer, the VideoTurtle, and an S-Video equipped TV,
you get equal or better display quality, than your old RGB monitor. Not
only that, you get a much bigger and eye-pleasing display, and a TV to
boot!

     The VideoTurtle, from Turtle Enterprises, can be purchased for
$149.95 from one of it's authorized distributors, such as Tex Comp Ltd.
To order all 1-800-846-3474. For technical information on TV RGB systems
we haven't mentioned, or general technical help, call 1-626-967-3341.
Turtle Enterprises can be reached via email: videoturtle@hotmail.com