STN-36

About initializing the hardware chip

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■Important/Strictly observed

Be sure to observe items and prohibited items that are explained in the manual as having undefined operations . These irregular operations and phenomena vary depending on the Sega Saturn compatible machine and hardware version. Therefore, be sure to initialize each hardware chip on the application side .

■Be careful

For VDP1, VDP2, and SCSP, the values set in BOOT-ROM (logo display, multiplayer screen, etc.) remain set in the hardware chip, so applications can use these values as default values. Be sure to initialize it before using it.

■Caution example

●Example 1: Notes on ECD and PSD bits in polygon drawing commands

When specifying a polygon drawing command, specify a fixed value of "1" for both ECD and SPD bits (bits 7 and 6) of the drawing mode word (CMDPMOD). If "0" is specified, the operation is undefined.

reference:

"HARDWARE MANUAL/VDP1 User's Manual"
7.7 Polygon drawing commands

●Example 2: Note about the Clip bit in the drawing mode word of each drawing command

If you set the drawing mode word (CMDPMOD) Clip bit (bit10) to 1 to use user clipping, be sure to issue the user clipping coordinate setting command. If the coordinates are not set, the value will be undefined.

reference:

"HARDWARE MANUAL/VDP1 User's Manual"
7.2 User clipping