picked out of the 16 color palette, but for each 8x1 area, only two colors could exist. When manipulating the screen in BASIC with the LINE command, one easily could exceed the maximum 2 colors per 8×1 area and end up with "color spill". Undocumented Texas Instruments originally only documented the four modes listed above. However the bit that enables mode 2 is more interesting than initially let on. It is best described as a modifier bit for the other modes. Enabling it does three things: Expands the color table size. Divides the screen horizontally into thirds. Changes two address bits of the pattern and color tables into mask bits, which controls whether each third of the screen has its own pattern and color table or not. With this in mind, three additional modes are possible. Note that although genuine TMS9918A chips support these modes, clones and emulators may not. Mode 0 (Text) + Mode 2 (Graphic 2): Known as Bitmap Text Mode. This mode allows for two-color bitmap images, with no color table. This saves memory, at the expense of a slightly reduced horizontal resolution (text mode has a horizontal resolution of 240 pixels instead of 256 pixels like the graphic modes do). Mode 1 (Graphic 1) + Mode 2 (Graphic 2): Known as Half-Bitmap Mode. Texas Instruments actually documented this "undocumented" screen mode in their manual titled "Video Display Processors Programmers Guide SPPU004". In section 8.4.2, "Playing Games with VRAM Addressing", they discuss how this mode combines the memory savings of mode 1 with the color detail of mode 2. However, as they go on to say this mode limits the number of sprites that can be displayed to 8 instead of 32. Therefore, the term "undocumented" used to describe this mode is a misnomer. However, because this manual was not widely known, this mode is generally considered to be one of the undocumented modes. Generally, the only reason to use this mode over Mode 2 is to reduce memory consumption. Mode 3 (Multicolor) + Mode 2 (Graphic 2): Known as Bitmap Multicolor Mode. This mode is more of a novelty, as it offers nothing beyond what the standard Multicolor mode can already do. Scrolling The TMS9918 does not have any scroll registers, and so scrolling must be done by software. Furthermore, scrolling can only be done on character boundaries, not pixel by pixel. Sprites Sprites are typically