No. There is a minor change to be made in the console which effectively puts the existing VDP "to sleep" and allows addressing video functions in the P-Box. No soldering is required.

The DIJIT Systems Advanced Video Processor Card is an advanced accessory for the TI-99/4A. It is installed in the Peripheral Expansion Box and functionally replaces the existing Video Display Processor in the console.

(Note: DIJIT is no longer in business)

There are two major factors affecting the resolution of a monitor, the bandwidth of the video amplifiers and the coarseness of the phosphor dots on the display screen.

Most TV sets can adequately display 40 column text and have a video bandwidth of approximately 3 to 4 Mz. But if you really examine the text displayed, you will find that the characters have a very "soft" appearance, that is, the edges of the characters are not sharp and well defined like those on a printed page. This softness is due to the electron beam not switching on and off abruptly. That little bit of time required to switch the electron beam on or off is referred to as "rise time". In the ideal world this time would be zero, but in the real world even the fastest events in nature take a certain amount of time. The closer we can approach the ideal, the shorter the on - off time, the crisper the edges of the characters displayed.

It can be shown mathematically that "rise time" and bandwidth are inversely related. That is, as the rise time approaches zero, the bandwidth of the video amplifiers required approaches infinity. We can rigorously calculate the characteristics of the video amplifier required by Fourier analysis, however for a quick estimate we can use a "rule of thumb": BW(MHz) ~ 500 / Tr (nsec).

The formula states that the amplifier bandwidth in Megahertz is approximately equal to 500 divided by the rise time of the pixel in nanoseconds. Typical Tr for the TMS9918A, TMS9928A, TMS9929A is 50 ns. So the video amplifier bandwidth required is approximately 10 MHz. The V9938 requirement is similar.

The other major factor determining resolution of a monitor is the screen of the cathode ray tube on which the data is displayed. There is generally no problem with a monochrome screen, be it amber, green or white. But the screen of an RGB display is consists of tiny dots of red, green and blue phosphors which are lit in various combinations and intensities. The glow is blended by the eye to give the appearance of the various colors of the spectrum.

The size of these dots in relation to the size of the screen determines the resolution of the CRT. Two common CRT sizes used in computer monitors are 12" (320 mm) and 14" (370 mm). These measurements are taken across the outside diagonal of the tube. The width of the displayable screen for these tubes is 243 mm and 280 mm respectively.

Many computer systems use 640 pixels horizontally for 80 column display by formatting the characters in an 8 x 8 pixel block. The V9938, however displays 80 columns using 512 pixels by formatting the characters in a 7H x 8V pattern. The 512 is exactly double the 256 used by the TI VDP for 40 column display and does not include an allowance for "backdrop" or overscan on either side of the computer generated image. Add approximately 90 pixels for backdrop for a total of 602 pixels displayed.

If we divide 370 mm by 602, we get a dot pitch of .6 mm which is the minimum spacing between adjacent pixels to display the 80 column text. Since the average TV picture tube has a dot pitch of .6 mm, it sounds great. However, having just enough pixels to light as there are generated by the computer or TV only works on those huge TV screens used in stadiums or other outdoor displays. It doesn't work with a CRT, especially if you sit very close to it and stare at it for an extended period of time.

You need about 25% more physical pixels on the face of the CRT to eliminate undesirable things like the "moire effect", the pattern we're most familiar with when we look through two window screens, one behind the other. This occurs because the computer generated image is never in perfect registration with the phosphor dots on the screen. On a 14" CRT, it's been found that .5 mm dot pitch makes for a marginal 80 column display. We recommend .42 mm dot pitch for comfortable viewing. Of course .31 mm is much better, but then the price is also much higher.

There you have it then, a 10 MHz minimum video bandwidth and a .42 mm maximum dot pitch are required for a comfortable RGB monitor. We recommend the Magnavox 8CM515, which has these characteristics, as the best value.

(Note: DIJIT is no longer in business)