SEGA SATURN DEVELOPER'S MANUAL

● Frame buffer switching mode register

Frame buffer change mode bit: frame buffer change mode (FCM), bit 1

Frame buffer change trigger bit: frame buffer change trigger (FCT), bit 0

 1 cycle mode

 Setting prohibited

 Manual mode (erase)

 Manual mode (change)

 Setting prohibited

 Setting prohibited

 Setting prohibited

 Manual mode 
 (Erase & Change)

VBE	FCM	FCT	Switch mode	Switch time
0	0	0	changes every 1/60 seconds
0	0	1	−
0	1	0	Erase next field
0	1	1	Change in next field
1	0	0	−
1	0	1	−
1	1	0	−
1	1	1	Erase with V blank, Change in next field

Double dense interlace enable bit: double interlace enable (DIE), bit 3

Double interlace plot line: double interlace plot line (DIL), bit 2

DIE	DIL	Race mode	Draw after next frame change
0	0	Non-interlaced / Single dense interlaced	All line drawing
0	1	Setting prohibited	−
1	0	Double dense interlace	Draw only even (EVEN) lines.
1	1	Double dense interlace	Draw only odd (ODD) lines

Even / odd coordinate select bit: even / odd coordinate select bit (EOS), bit 4

EOS	Even / odd coordinate selection bit
0	sample even pixels only
1	Only the pixels with odd coordinates are sampled.