you'll recall from the previous page, an electron gun located
at the back of a CRT shoots a tightly knit set of electron
beams past two deflecting magnetic fields towards a phosphor
coated screen. When the phosphors are struck by electrons
they give off light (red, green, and blue).
In order for all this to happen, a color
raster CRT needs five signals: one for electrons that excite
red phosphors, one for electrons that excite green phosphors,
one for electrons that excite blue phosphors, one to steer
/ deflect the electron beam from right to left, and one
to steer / deflect the electron beam from top to bottom.
On a standard VGA connection these five signals travel on
pins 1, 2, 3, 13, and 14, respectively.
Pins 1, 2, and 3 control when and how the
electron gun fires. If the monitor doesn't receive a signal
from one of these pins, no electrons fire, and no light
is produced. If the monitor receives a signal from one of
these pins, however, the respective electron beam fires
and an active pixel is produced (one that gives off light).
Stronger signals (measured in volts) instruct the electron
gun to fire more electrons. Consequently, by varying the
strength of the signal sent down each pin, a pixel of any
color or intensity can be produced.
Pins 13 and 14 control the timing of the
magnetic fields that steer the electron beam from left to
right and from top to bottom. Pin 13 sends the horizontal
synchronization signal (hsync for short) which ultimately
causes the electron beam to flyback and start the next scanline.
Pin 14 sends the vertical synchronization signal (vsync
for short) which ultimately causes the electron beam to
flyback and start the top scanline.
You can see how all these signals work
together by studying the operation of our theoretical CRT
above. Signals sent on pins 1, 2, and 3 instruct the CRT
to fire the electron gun. The electron beams fired from
the electron gun strike the CRT's phosphor coated screen
and produce active pixels (pixels that give off light).
Shortly after the signals on pins 1, 2, and 3 end, however,
pin 13 sends a horizontal synchronization signal which ultimately
causes the electron beam to flyback and start the next scanline
(in essence, it resets the magnetic field potential horizontally).
Near the last scanline of the frame, pin 14 sends a vertical
synchronization signal which ultimately causes the electron
beam to flyback and start the top scanline (in essence,
it resets the magnetic field potential vertically). This
whole process repeats, refreshing the screen so many times
per second. Like motion pictures, it all happens so fast
that the naked eye can't see it.
All color raster CRTs require the above
five signals to operate. Unfortunately, TVs, arcade monitors,
and PC monitors use different methods for receiving these
On a VGA video card, pins 1 (red), 2 (green),
and 3 (blue) send signals between 0 - 0.7 volts. Traditional
arcade monitors require a 1 - 5 volt signal for red, green,
and blue. This is why VGA to arcade monitor setups usually
require a video amplifier, without the amplifier images
On a VGA video card, signals sent on pins
13 and 14 affect the timing of the deflecting magnetic fields.
Pin 13 instructs a PC monitor to reset the magnetic field
horizontally and pin 14 instructs a PC monitor to reset
the field vertically. On some arcade monitors these two
signals run on the same wire. This is why pins 13 and 14
are sometimes wired together on a VGA to arcade monitor
TVs are a whole different ball game. On
a composite connection all five signals are sent down the
same wire. On an S-Video connection the five signals are
split up between two wires, one for luminance information
and the other for crominance information. This means that
a simple video amplifier isn't going to cut it for a VGA
to TV setup. You not only need to change the voltage of
the data signals, but marry them together so that they travel
on the same wire harmoniously. This is normally done via
a VGA to TV scan converter. And ya, scan converters aren't
cheap. As most modern video cards now feature S-Video out,
it's very, very easy to run Windows MAME on a TV. Just connect
the S-Video out on your video card to your TV's S-Video
in port. Note, AdvanceMAME will NOT work through TV-out.