TMS9918

The TMS9918 is a video display controller (VDC) manufactured by Texas Instruments and introduced in 1979. In TI's manuals it's called a "Video Display Processor" (VDP). The TMS9918 and its variants are used in the Casio PV-2000, Coleco Adam, ColecoVision, CreatiVision, Hanimex Pencil II, MSX, Memotech MTX, NABU Personal Computer, PECOS, SG-1000, SC-3000, SV-318, SV-328, Sord M5, TI-99/4, Tatung Einstein, and Tomy Tutor.

The TMS9918 was an advanced design for the era. It had four graphics modes based on an underlying 256 wide by 192 high pixel layout, which could be used as a 40 by 24 character display, a 256 by 192 pixel display, or a 64 by 48 pixel display which used less memory. It had a fixed color palette with 15 colors plus transparent. It also supported 32 single-color 8x8 or 16x16 pixel sprites, numbered 0 to 31, with lower-numbered sprites appearing on top of higher-numbered ones. This allowed for layering and perspective effects. It also featured a video input and sync pin, which allowed video from another source to appear under the graphics being created by the chip. This could be used to layer the output from multiple 9918's, or to use the 9918 as a system for titling and overlays on other video sources.

To support this advanced feature set, the 9918 required fast access to memory. To allow this, it was given a dedicated 16 KB pool of RAM that was separate from the main memory of the computer that it was part of. TI referred to this as VRAM. This meant that the CPU could only update the video display over a separate 8-bit data bus with the VDP moving data on the bus to and from its dedicated RAM. This limited the speed at which the CPU and 9918 could communicate. It also meant that the common solution of using the video chip to refresh memory could not be used and had to be implemented in separate hardware. While these represented minor complications compared to systems that shared memory in a single pool, the result was a display that was much more colorful and offered some parity with arcade game-level displays.

The Yamaha V9938 is an enhanced version of the TMS9918.