■ 2.2 Table on VRAM

● Command table

• The command table is a table in which commands are defined in VRAM, and VDP1 reads the commands to draw parts and perform clipping processing.

• The command is:
  Drawing command:
  It is divided into texture drawing and non-texture drawing, and each has a fixed sprite, a rectangular sprite, a deformed sprite drawing command, a polygon, a polyline, and a line drawing command, and draws these parts.

  Clipping coordinate setting command:
  There are user clipping and system clipping coordinate setting commands to set the drawing area of the part.

  Relative coordinate setting command:
  Specify to define the drawing coordinates of the part as relative coordinates.

  Drawing end command:
  Finish drawing.

  The size of the command table is 1EH (30) Byte and the boundary is 20H (32) Byte.

  Each command is loaded into VDP1 and processed individually. This operation is called fetching.

  The command table is fetched from the VRAM start address (000000H), and the next command table is fetched according to the jump format specification.

  The color lookup table, Gouraud shading table, and character pattern table are referenced as specified in the command table.

● Color look-up table

• It is a table that defines 16-bit 16-color color code on VRAM.

• When the color mode is used in the lookup table method with the texture drawing command, it is referenced as color data.

• The pixel data of the character pattern is converted to a color code and written to the frame buffer.

• The size is 20H (32) Byte and the boundary is also 20H (32) Byte.

• It is referenced by the lookup table address indication of the texture drawing command.

● Gouraud shading table

• This is a table that defines 16-bit 4-point RGB codes on VRAM.

• It is referenced when Gouraud shading processing is specified by color calculation in the drawing command of the part.

• The pixel data of the part is Gouraud-shaded and written to the framebuffer.

• The size is 8HByte and the boundary is also 8HByte.

• It is referenced by the instruction of the Gouraud shading table address of the drawing command of the part.

• When applying Gouraud shading, the pixel data of the part is limited to RGB code. Results are not guaranteed for color bank codes.

● Character pattern table

• It is a table in which pixel data of character pattern is defined on VRAM.

• It is referenced by the texture drawing command.

• Pixel data is defined as 4, 8 and 16bit / pixel color data according to the color mode specification.

• The pixel data of the character pattern is added with a color bank in the color bank mode, converted by the color lookup table in the color lookup table mode, and written to the frame buffer as it is in the RGB mode.

• The size is determined by the character size and color mode. The boundary is 20H (32) Byte.

• It is referenced by the character address instruction of the texture drawing command.