SEGA SATURN DEVELOPER'S MANUAL

1-cycle mode

Erase (manual mode)

The CPU controls the 1-frame erase light.
Manual erase write of the frame buffer is specified by writing to the register with VBE = 0, FCM = 1, FCT = 0. The display frame buffer is erased at the next specified field, and the display frame buffer is cleared.
The frame buffer for drawing and display is not switched. Since the display frame buffer is cleared when erasing is performed, it is necessary to switch between drawing and display by specifying a change in the next field where erasing is specified.
Use this mode when there are 2 fields or more and 1 frame, such as double dense interlace. Also, when switching from manual mode to single cycle mode, this erase is used in the field before switching.
Erase is used when you know that you want to change frames in the next two fields. If the frame change is unknown until the previous field, use erase and change.

Change (manual mode)

The switching of one frame is controlled from the CPU.
Switching is specified by writing to VBE = 0, FCM = 1, FCT = 1. The next specified field will be switched between drawing and display.
Erase write is not performed, so it is necessary to erase the frame buffer by specifying erase in the field immediately before specifying the change.
Characters can be drawn on the back side until switching is instructed.
Normally, use this change when switching from 1-cycle mode to manual mode. Use this change when switching the frame buffer in manual mode.