FF90 = Init register 0 Bit 7 0=GIME video 1=VDG video Bit 6 MMU enable (0=off 1=on) Bit 5 IRQ enable Bit 4 FIRQ enable Bit 3 Vector RAM enable Bit 2 SCS (0=xpand 1=normal) Bit 1 /ROM mapping Bit 0 \ 0X = 16K internal, 16K external 10 = 32K internal 11 = 32K external FF91 = Init register 1 Bit 7 NA Bit 6 0=64K X 4, 1=256K X 1 DRAMS Bit 5 Timer clock 0=63us 1=70ns Bit 4 NA Bit 3 NA Bit 2 NA Bit 1 NA Bit 0 MMU register set select FF92 IRQ Enable register FF93 FIRQ Enable register Bit 7 NA Bit 6 NA Bit 5 Timer Bit 4 Horizontal sync Bit 3 Vertical sync Bit 2 RS232C data input Bit 1 Keyboard/Joysticks Bit 0 Cartridge interrupts FF94 Timer MSB FF95 Timer LSB FF96 NA FF97 NA FF98 Video mode register Bit 7 0=text 1=graphics Bit 6 NA Bit 5 descender enable (txt) Bit 4 monochrome(1)/color(0) Bit 3 50hz / 60hz sync Bit 2 \ Bit 1 - Lines/text row Bit 0 / 000 = 1 line 001 = 2 lines 010 = 3 lines 011 = 8 lines 100 = 9 lines 101 = 10 lines 110 = 11 line 111 = 12 lines FF99 Video Res Register Bit 7 NA Bit 6 Scan lines, bit 1 Bit 5 Scan lines, bit 0 Bit 4 Horizontal res, bit 2 Bit 3 Horizontal res, bit 1 Bit 2 Horizontal res, bit 0 Bit 1 Color bit 1 Bit 0 Color bit 0 for: Colors HR2 HR1 HR0 CO1 CO0 --------------------------------- 640 4 1 1 1 0 1 640 2 1 0 1 0 0 512 4 1 1 0 0 1 512 2 1 0 0 0 0 320 16 1 1 1 1 0 320 4 1 0 1 0 1 320 2 0 1 1 0 0 256 16 1 1 0 1 0 256 4 1 0 0 0 1 256 2 0 1 0 0 0 160 16 1 0 1 1 0 FF9A Border color register FF9B NA FF9C Vertical fine scroll register FF9D Screen start address Bits 18-11 FF9E Screen start address Bits 10-3 DDDDDDDDEEEEEEEE000 FF9F Horizontal offset register Bit 7 128byte screen enable Bit 6 \ Bit 5 \ Bit 4 \ 0-127 byte offset from Bit 3 - FF9D/FF9E Bit 2 / Bit 1 / Bit 0 / FFA0-FFA7 MMU task set 0 FFA8-FFAF MMU task set 1 FFB0-FFBF Palette Registers xx xx R1 G1 B1 R0 G0 B0