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VDP1 User's Manual/Chapter 5 Table

■5.4 Command table

The command table consists of 1EH (30) Bytes. The command table is fetched every 20H (32) Bytes, so please define it with a 20H boundary. The 2 bytes following the command table are dummy and are skipped when fetching the command table.
The command table stored in VRAM is fetched from the start address (00000H) for each frame. Be sure to store the command table in addresses 00000H to 0001EH. If you place something other than a command table (color lookup table, Gouraud shading table, character pattern table), drawing behavior is not guaranteed. VRAM is up to address 7FFFFH. Do not define Gouraud shading tables beyond address 80000H.

Figure 5.5 Command table
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CMDCTRL +00H END JP ZP 0 0 Dir Comm
CMDLINK +02H LINK specification/8H 0 0
CMDPMOD +04H MON 0 0 HSS Pclp Clip Cmod Mesh ECD SPD color mode color calculation bit
CMDCOLP +06H Color bank, color lookup table/8H (LSB fixed at 00B), non-texture
CMDSRCA +08H Character address/8H 0 0
CMDSIZE +0AH 0 0 Character size X/8 Character size Y/8
CMDXA +0CH sign extension Vertex (A), X coordinate (XA) *
CMDYA +0EH sign extension Vertex (A), Y coordinate (YA)
CMDXB +10H sign extension Vertex (B), X coordinate (XB)
CMDYB +12H sign extension Vertex (B), Y coordinate (YB)
CMDXC +14H sign extension Vertex (C), X coordinate (XC)
CMDYC +16H sign extension Vertex (C), Y coordinate (YC)
CMDXD +18H sign extension Vertex (D), X coordinate (XD)
CMDYD +1AH sign extension Vertex (D), Y coordinate (YD)
CMDGRADA +1CH Gouro shading table/8H
+1EH Dummy (will be skipped when fetching the table)
+20H subsequent table
+40H subsequent table
+60H :
:

[Note] * The first bit of the vertex coordinate is the sign bit. Negative values are expressed in two's complement. Extend the sign of the upper 6 bits.

The drawing order of each part, such as sprites, is determined by how this command table is placed in VRAM.
The drawn parts processed first are the ones furthest from the viewpoint, and the drawn parts processed last are the ones closest.

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Copyright SEGA ENTERPRISES, LTD., 1997