General Information
The TMS9918 was used in systems like ColecoVision, CreatiVision (Japanese variant), Memotech MTX, MSX, Sega SG-1000/SC-3000, Spectravideo, Sord M5, Tatung Einstein, Texas Instruments TI-99/4 and Tomy Tutor/Pyuuta. Modified versions with additional display modes and registers were used in the Sega Master System, Sega Game Gear, and the Mega Drive. (Note that the Mega Drive VDP cannot access any of the TMS9918 display modes discussed below.) The TMS9918(A) also featured an external composite video input which made it a handy chip to use in video "titlers" that could overlay text or graphics on video.
There are several variants called TMS9918A, TMS9928A and TMS9929A, where the 'A' indicates a second version of the chip which added new features, most prominently the addition of a bitmap mode (Graphic II). The non-A version was only used in the TI-99/4; the TI-99/4A and the other computers had the A version VDC. The TMS9918A and TMS9928A output a 60Hz video signal, while the TMS9929A outputs 50Hz. The difference between '1' and the '2' in 'TMS9918A' and 'TMS9928A' is that the '1' version outputs composite NTSC video, while the '2' versions (including the TMS9929A) outputs YPbPr, more precisely the Y, R-Y and B-Y colour differences (luminance and colour difference signals). The need for the latter was predominant in the 50Hz world, including Europe, due to the different video signal standards PAL and SECAM. It was more cost-effective to output Y, R-Y and B-Y and encode them into PAL or SECAM in the RF modulator, than to try and have a different console for every different color standard. All of the ICs in this family are usually referred to by the TMS9918 name, sometimes with an 'A' postfix.
Texas Instruments' TMS9918A was succeeded by Yamaha's V9938, which added additional bitmap modes, more colorful sprites, a vertical scroll register and a customizable palette. The V9938 was used in a third-party upgrade to the TI-99/4A — the Geneve 9640 'computer-on-a-card'. The V9938, in turn, was succeeded by the V9958, which added some additional high-colour modes and a horizontal scroll register. These chips were used in the "TIM" upgrade card for the TI-99/4A, as well as on the MSX 2 and MSX 2+/turboR systems, although rumor has it that the V9958 was also used in a generation of the Photo Play arcades. Yamaha also produced a V9990, which is considered the follow-up of the V9958 by some, but it is not backwards compatible. A graphic chip extension utilizing the V9990 exists for the MSX in the form of the 'Graphics9000' cartridge by Sunrise.
A later variant of the TMS9918 series chips, the TMS9118, TMS9128, and TMS9129, were released in the mid-late 1980s, but were never very popular. The function of one pin is changed, and a different mapping of the 16k × 8 bit block of video memory is supported. Otherwise the chips are completely identical to the TMS9918A, TMS9928A and TMS9929A respectively.
Read more about this topic: Texas Instruments TMS9918
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