The flash carts sold by Bung on power up appear like an MBC5 cart except that writing $00 to the bank select register selects rom bank 1 instead of rom bank 0. Writing values to 3000-3FFF area does nothing in 4 and 16 MBit carts. Writing values (XXXXXXXS - X = Don't care, S = Select) to 6000-7FFF area selects MBC1 16/8 mode if S=0 except that writes to 3000-3FFF area still do nothing in 4 and 16MBit carts. If S=1 then MBC5 mode is selected. (S=1 by default on power up.) Cart locations A000 & A100 act as special write only hardware control registers if a value of $c0 is written to 0000-1FFF area. These hardware control registers are used for setting up cart hardware for different games when the Bung cart is used as a Multicart for holding several different games. Here is a part of the Bung Multicart Menu code and this seems to be where control is given from the menu to one of the various games in the cart. This routine is copied to RAM & executed in RAM while cart bank reconfiguration is taking place. Four parameters are passed in C001,C002,C003,C004 that define hardware parameters for the selected game. ; c000 = Cart RAM($80)/No Cart RAM($00) ; c001 = ROM Usage (0=32k,1=65k,3=128k,7=256k,f=512k,1f=1M,3f=2M) ; c002/hi nibble = RAM Usage (0=8k,3=32k) ; c002/lo nibble = RAM bank 0 offset in SRAM (8k byte increments) ; c003 = ROM bank 0 offset in Flash (32k byte increments) ; (Menu uses 0 so must be 1 or greater.) l0bda: di ; 0bda f3 s ld a,0 ; 0bdb 3e 00 >. ldh (0ffh),a ; 0bdd e0 ff `. ld a,0ah ; 0bdf 3e 0a >. ld (l0000),a ; 0be1 ea 00 00 j.. ; Switch to cart bank reconfigure mode ld a,0c0h ; 0be4 3e c0 >@ ld (l0000),a ; 0be6 ea 00 00 j.. ld a,0a1h ; 0be9 3e a1 >! ld (0a000h),a ; 0beb ea 00 a0 j. ld a,(0c001h) ; 0bee fa 01 c0 z.@ ld (0a100h),a ; 0bf1 ea 00 a1 j.! ld a,0a2h ; 0bf4 3e a2 >" ld (0a000h),a ; 0bf6 ea 00 a0 j. ld a,(0c002h) ; 0bf9 fa 02 c0 z.@ ld (0a100h),a ; 0bfc ea 00 a1 j.! ld a,0a3h ; 0bff 3e a3 ># ld (0a000h),a ; 0c01 ea 00 a0 j. ld a,(0c003h) ; 0c04 fa 03 c0 z.@ ld (0a100h),a ; 0c07 ea 00 a1 j.! ld a,0a0h ; 0c0a 3e a0 > ld (0a000h),a ; 0c0c ea 00 a0 j. ld a,0c0h ; 0c0f 3e c0 >@ ld (0a100h),a ; 0c11 ea 00 a1 j.! ld a,0 ; 0c14 3e 00 >. ld (l4000),a ; 0c16 ea 00 40 j.@ ld a,0a0h ; 0c19 3e a0 > ld (0a000h),a ; 0c1b ea 00 a0 j. ld a,(0c000h) ; 0c1e fa 00 c0 z.@ ld (0a100h),a ; 0c21 ea 00 a1 j.! ; Exit cart bank reconfigure mode ld a,0ah ; 0c24 3e 0a >. ld (l0000),a ; 0c26 ea 00 00 j.. ; Clear video ram ld hl,8000h ; 0c29 21 00 80 !.. ld de,l2000 ; 0c2c 11 00 20 .. ld a,0 ; 0c2f 3e 00 >. ldh (40h),a ; 0c31 e0 40 `@ l0c33: ldh a,(41h) ; 0c33 f0 41 pA and 2 ; 0c35 e6 02 f. jr nz,l0c33 ; 0c37 20 fa z ld a,0 ; 0c39 3e 00 >. ldi (hl),a ; 0c3b 22 " dec de ; 0c3c 1b . ld a,d ; 0c3d 7a z or e ; 0c3e b3 3 jr nz,l0c33 ; 0c3f 20 f2 r ; Setup default video mode ld a,91h ; 0c41 3e 91 >. ldh (40h),a ; 0c43 e0 40 `@ ; Initialize the stack ld sp,0fffeh ; 0c45 31 fe ff 1.. ; Execute selected game in the multicart jp l0100 ; 0c48 c3 00 01 C..