Caltron / Myriad Games 6 in 1 Mapper #41 Info --------------------------------------------- 03.29.2000 V1.00 Mapper info by The Mad Dumper Thanks to AlanD for drawing out the schematic for me and to Thomas S. for implementation help --- OK, this is one sadistic mapper circuit. There are two registers on it... I will call them Reg1 and Reg2 for simplicity sake. When the NES is switched on, or the reset button is pressed, both registers are cleared to 00h. There is a cool little diode / RC circuit on the M2 line that does this. ------------------------ Reg1 is the "main control" register. It has six bits. You write to it by writing a byte to 06000h thru 067ffh. Like other multicarts, the address lines are used instead of the datalines, and the value of the byte written has no effect. A0 = bit 0, A1 = bit 1, etc. A0-A5 are used: Bits: 0 - PRG 0 1 - PRG 1 2 - PRG 2 / enable second register * (see text) 3 - CHR 2 4 - CHR 3 5 - Mirror control. 0 = V, 1 = H PRG 0-2 specify a 32K PRG bank that appears at 8000-FFFF. Note that the banks are 32K in size, and there are 8 of them for a total PRG size of 256K bytes. Bit 2 is strange. When it is 1, it enables writes to the second register. ------------------------ Reg2 is the "auxilary CHR control" register. It only has 2 bits. You write to it at 08000-0ffffh. Writes are only accepted if bit 2 of reg1 is set. Writes are rejected if this bit is 0! Unlike the above register, writes this one relies on what is written instead of the address it is written to. Bits: 0 - CHR 0 1 - CHR 1 CHR bits 0,1 (from this register) and bits CHR bits 2,3 (from reg1) select the desired bank for the CHR ROM. There are 16 8K banks for a total of 128K bytes worth of CHR ROM ------------------------ Last notes: The game "Cosmo Cop" seems to exploit a PPU bug of some form or another. It checks the sprite0 hit flag, while sprites are turned off!! So, on emulators it locks up after showing the title screen. If the hit flag is turned on while sprites are disabled in the emulator, the game (and the other 5 on the cart) work flawless. So, some more PPU research may be in order.