As 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 signals.

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 appear dim.

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 setup.

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.