Was this meant to be a 2-in-1 MMC3 multicart with two 2x128kB games? Clues on the reason for the 4kB UVEPROM?
very similar (if not identical) to Super Mario Bros 16 which has PRG/CHR address lines mixed and MMC3.A0=CPU.A3
The big PCB:
Hard to tell without knowing how the signals underneath 74.. chips go.
* 2C and 2D are 128k PRG/CHR mask roms with pin1 = A16 and pin 22 = A15
* 27C512 is 64k CHR one-time programmable EPROM with regular pinout (pin1 = A15)
* tracks under 2732 shows it was not prepared for more than 8k
* blob is MMC3 with standart pinout & connections
I think 2C and 2D are PRG/CHR of regular Jackie Chan, 27512 adds mario graphics to it and 4k EPROM is some patch for PRG that allows the game with altered MMC3 registers (MMC3.A0=CPU.A3) to work on regular connection.
Similar patch in additional EPROM like in Don Doko Don 2.
I can definitely say that there is no jump or vector into the $6000-$7FFF area. It dumps as normal TLROM.
Edit: Trying to dump the $6000-$7FFF area results in 6000 being 00 and the rest of the range having $ff on the first read, and on any of the subsequent reads, the whole range containing solely $ff, which I assume is open bus behavior.
Yes, sorry.You mean Don Doko Don
I think the "patch" is done on the fly, without jumping, that is - when accessing to some range of ROM address, the additional logic enables the "patched ROM" instead of the original one, this probably occurs for PRG and CHR.I can definitely say that there is no jump or vector into the $6000-$7FFF area. It dumps as normal TLROM.
Do you have dump of the cartridge? I would like to compare it against:
Country_Unk\Super Bros 10 Kung Fu Mari.nes
Japan\Jackie Chan (J) [a1].nes
Japan\Jackie Chan (J).nes
For example, looking at the ROM offsett 1FFE0 shows that the signature ("JACKIE CHAN") is in different offsets. So those 2 versions of Jackie Chan are probably complete different builds and Super Bros 10 is a patched "Jakcie Chan" of yet another built.
I compared Super Bros 10 Kung Fu Mari.nes against USA\Jackie Chan's Action Kung Fu (U).nes and they seems to be almost same, differences, here are difference regions:
D65B-D698 copyright information cut off
1C284, 1C292, 1C737 (*)
1DD18, 1E1AB, 1E1B1, 1E1DF, 1E20F, 1E215, 1E29B, 1E2D0, 1E3AC, 1F53B, 1F548, 1F6E8, 1F83A, 1FD72 (*)
(*) = those refers to the fact that Jackie Chans Use 8001/E001/C001 while Super Bros 10 - 8005/E005/C005 (which is irrelevant cause for MMC3 is the same)
2E111-38B9A (less than 64k)
No idea why the patch and whole logic instead of just putting EPROMs with altered PRG/CHR.
Assuming they wanted to patch the above regions marked as (?), they needed to cover those 2 regions:
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$0f800-$0ffff = 011111xxxxxxxxxxx $1c800-$1cfff = 111001xxxxxxxxxxx |||||| |||||+- CPU A11 ||||+-- CPU A12 |||+--- MMC3 PRG A13 ||+---- MMC3 PRG A14 |+----- MMC3 PRG A15 +------ MMC3 PRG A16
Connecting 2732.A11 to MMC.A16 causes the first 2 kB of 2732 EPROM to store the first region and the second 2kB the other.
By dividing the whole CHR into eight 16k regions and counting how many bytes in that regions differ shows that there are only four regions that need to be patched.
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region # diffs $00000-$03fff: 0 000 $04000-$07fff: 0 001 $08000-$0bfff: 0 010 $0c000-$0ffff: 2747 011 - fourth 16k in 27c512 $10000-$13fff: 4660 100 - first 16k in 27c512 $14000-$17fff: 3248 101 - second 16k in 27c512 $18000-$1bfff: 1118 110 - third 16k in 27c512 $1c000-$1ffff: 0 111 ||| ||+- MMC3 CHR A14 |+-- MMC3 CHR A15 +--- MMC3 CHR A16
The missing 7402, if soldered (without 74138/7432/7400) makes the PCB usable as regular MMC3 with two 64K standard CHR-EPROMS. There must be some jumpers underneath CHR-ROM however that disconnects MMC3-CHR-A16 from its pin1.
There is no way to read-back unmodified parts of 2C and 2D mask roms without cutting some traces or desoldering them.
If this cartridge was from 88 or earlier, I would say that huge EPROMs were expensive and making all that "patching" using smaller ROMs was more economical to save money than using four 27512 (or two 27010) chips.
But basing on the manufacturing dates of chips (1992) plus all the 74 logic which costs and time needed to design PCB makes me think that this is rather some kind of copy-protection - author assumed that somebody who would like to duplicate this cartridge will need not only to read-back eproms, but also analyze the circuitry. I doubt this PCB can be used for any other game.