SEGA SATURN DEVELOPER'S MANUAL

■ Frame buffer rotation readout

By reading the frame buffer diagonally, the entire frame buffer plane can be rotated.
Parts whose display coordinates exceed the frame buffer address range are treated as transparent (XX00H at 8bit / pixel, 0000H at 16bit / pixel).
The clipping area and erase light area are fixed relative to the frame buffer plane even if the frame buffer is rotated and read. Therefore, the clipping area and erase light area are inclined with respect to the display screen.
To prevent the display screen from being lost even when the frame buffer is rotated, the coordinate range of the frame buffer must be increased. In this case, the frame buffer is set to 8bit / pixel, and the screen is set to 512x512 instead of 512x256. The number of simultaneous colors can be up to 256.
Rotation is prohibited when normal, high-resolution, HDTV, or double-dense interlace is set.
Reading start coordinates and reading movement value for frame buffer rotation reading are received from VDP2.
The frame buffer rotation readout is valid only at rotation 16 and rotation 8. Otherwise it is prohibited. Even if rotation data is sent from VDP2 during non-rotation, it is invalid and the VDP1 parameters are valid.