In the case of displays that work like the 68047, the screen, depending on the resolution, is divided into a matrix or grid of tiny color squares or dots. Each dot on the screen occupies a particular bit in a byte of screen display memory. The color of a particular dot is also encoded in bits of the display RAM. This encoding of dots and color is called memory partitioning.


Fig. 2-15. The ultimate color graphics display using the 68047 vdg chip.

Fig. 2-16 shows how the 68047 partitions memory for the 10 different text and graphics modes. As you can see from the drawing as the density of the display increases, more bytes are required to hold the entire screen and this results in a more costly computer product. This figure is a detailed description of how the vdg partitions its display memory. The highest resolution is Graphics 7, with 256 columns by 192 rows. Here 6144 bytes of RAM are required. Each bit in the data word from display RAM specifies a single location on the screen, which may be one color (green or blue). One level down, Graphics 6, uses the same number of bytes, cuts maximum columns to 128 (from 256) but any one dot may be one of four colors. Your software could be assembly or BASIC.

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