TMS9918

[1] The TMS9918 and its variants were used in the ColecoVision, CreatiVision, Memotech MTX, MSX, NABU Personal Computer, SG-1000/SC-3000, Spectravideo SV-318, SV-328, Sord M5, Tatung Einstein, TI-99/4, Casio PV-2000, Coleco Adam, Hanimex Pencil II, PECOS and Tomy Tutor.

The TMS9918 generates both grid-based character graphics (used to display text or background images) and sprites used for moving foreground objects.

The key features of this chip are, as highlighted in a 1980 presentation by Karl Guttag (one of the designers):[1] All of the ICs in this family are usually referred to by the TMS9918 name, sometimes with an 'A' postfix.

The 'A' indicates a second version of the chip which added new features, most prominently the addition of a bitmap mode (Graphic II).

The need for the latter was predominant in the 50 Hz world, including Europe, due to the different video signal standards PAL and SECAM.

Due to the large die size and relatively high internal speed, the TMS9918 ran warm enough to necessitate a heat sink; some devices such as the Taiwanese DINA console (a hybrid Colecovision/SG-1000) neglected to install sinks and suffered from malfunctions of the chip.

Another popular use is to create a second copy of some or all of the display data to eliminate flickering and tearing, a technique known as double buffering.

As a data byte is written or read, the TMS9918 automatically increments the internal address register.

By sequentially printing the characters 0 through 255 in all three areas, the program can simulate a graphics mode where each pixel can be set individually.

The CPU then jumps to a sprite-handling routine in the software, which in turn tells the VDP where to reposition the sprites.

Due to the fact that in practice this one step will never be done alone, it's no problem that some results will be negative: Next comes the conversion to RGB.

All results must be in the range from 0% to 100%: The erroneous value of 113% for R of color "light red" might seem to come from a typo within the datasheet and there R-Y must not be greater than 80%.

Up to that time only cathode ray tubes had been available for computer monitors as well as for televisions, and that these CRTs had a gamma.

Texas Instruments' TMS9918A was succeeded by Yamaha's V9938, which added additional bitmap modes, more colorful sprites, a vertical full-screen scroll register, vertical and horizontal offset registers, a hardware blitter and a customizable palette.

The V9938, in turn, was succeeded by the V9958, which added some additional high-colour modes and a horizontal two-page scroll register, these chips were used in the MSX2+/turboR systems.

Toshiba made a clone called the T6950 and does not support the undocumented pattern / color table masking feature in graphics 2 mode.

[5][better source needed] Later, Toshiba released the T7937A MSX-Engine with a built-in VDP and fixed the masking features.

The TMS9918 was the basis for the VDP chips in the Master System, Game Gear, and Mega Drive (Genesis).

[citation needed] They use additional display modes and registers, and added hardware scrolling capabilities and other advanced features.