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PostPosted: Mon Jun 24, 2019 7:56 am 
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Joined: Sun Jun 12, 2011 12:06 pm
Posts: 540
Location: Poland
[review+reverse engineering] Pirate Mini NES

While walking on the flea market, I noticed a guy selling NES console. He wanted 1.25$ so I considered it a good deal.
It must have been repaired by some hobbyist electrician, because of those loose banana jacks soldered in place of DC connector.
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I quickly realized it is not original NES because of its small size, but it is also neither mini-NES because of the presence of cartrige connector.
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I couldn't wait to open it and see what's inside - and there is fully chipped PCB! There is also additional internal ROM with games, executed when no cartridge is present. Cool - never seen famiclone with build-in games that was neither blob nor dual slot unit. Looks like the designer was inspired by Atari 2600 Rambo.
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7805's radiator was soldered upside down causing the gigantic thing to rely only on 3 solder pads (which ultimately were gone).
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I though of making reverse-enginner proces to find out how the cartridge detection works and to dump the internal ROM.
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* It works in Dendy Mode like all famiclones (not PAL). CPU = TA-03NP1, PPU = TA-02NP - no duty cycle bug.
* Detection of external cartridge by checking if pins 1 and 72 (GNDs) are shorted.
* Internal cartridge = 22 games + 22 games (with donkey kong theme)
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Mapper of internal cartridge is:
Code:
PRG = 256K + 256K (switched by reset), CHR = 8K RAM
$8000-$FFFFL [MMvPPPPP]
              ||||||||
              |||+++++- PRG bank (lowest bit ignored in 32k MODE)
              ||+------ PRG mode (0=32K, 1=16K)
              ++------- mirroring (00 = Scr0, 01=V, 10=H, 11 = Scr1)

* There is no stupid shelf, the cartridge is placed horizontally directly into the connector. Simple and reliable - every NES cartridge that I own works from first run. Eject mechanism is also simple and robust.
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* D3 and D4 of both joypad ports are wired to $4017.
* There is $4016.D1, $4017.D1, $4017.D2 but it is just wired to pull-up and does not go anywhere. OUT1/OUT2 not wired.
* No CIC
* The clock generating circuit for CPU & PPU is like in original Famicom, but there is unpopulated place for DIL16 and DIL14 - maybe someone can guess what can be put there? Pinout suggest ordinary 74xx or 4xxx chips, but the signal does not go anywhere else (alternative clock generator?)
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BTW. So good that there were banana jacks included, I will be able to replace to finally fix my old fatigued multimeter probes :D
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PostPosted: Mon Jun 24, 2019 9:19 am 
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Joined: Thu May 19, 2005 11:30 am
Posts: 975
krzysiobal wrote:
[code]PRG = 256K + 256K (switched by reset),
Sure it's not 512+512 KiB? Because you have five P bits, which would make a 512 KiB inner bank. If it is 512+512 KiB, then it would be iNES Mapper 233 (very out-dated description).

A variant of this ROM is in GoodNES 3.23b as "Super 22-in-1 [p1].nes". The GoodNES ROM has different games in the "Super 20 in One" part --- number 3 is "B-Wings", while it is "Mach [Rider]" in yours.


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PostPosted: Mon Jun 24, 2019 9:48 am 
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Joined: Sun Jun 12, 2011 12:06 pm
Posts: 540
Location: Poland
Quote:
Sure it's not 512+512 KiB?

You're right, thanks.


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PostPosted: Tue Jul 02, 2019 9:26 am 
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Joined: Wed May 04, 2011 2:41 pm
Posts: 425
Location: Montréal, Canada
Nice find! I had that exact same multicart when I was a kid (still have it). It's very nostalgic to see and remember the song perfectly. You would switch page with the reset button.


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