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Atari Flashback 2 Reverse Engineered Schematic


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I made a schematic of the Atari Flashback 2 based on reverse engineering a rev C board. 

 

https://github.com/alanbog/FB2-Schematic/

 

I'm hoping to find answers to some questions like:

  • How do you get RGB output?
  • If PB0, PB1, PB3, PB6, and PB7 are used for the buttons, and PB2 is used to switch between booting to the menu vs a cartridge, what do PB4 and PB5 do if anything?
  • What does a dump of the ROM look like? Part of it should contain code for the "Gizmo" menu system (which I've seen referred to as GizCode). 

 

 

The pinout of the Michele IC came from Curt Vendel's post here: 

A few of the pins don't appear to be accessible from outside of the epoxy blob, and I have no idea what most of them do. They are presumably left unconnected, but they could also be connected to GND or 3.3V under the blob. Interestingly, you can see test points for these pins in a prototype that Curt posted a photo of here: 

 

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I tested the functionality of PB2 (J2) and PB5 (J4) and they didn't appear to do anything in the menus or in games as far as I could tell.

 

PB4 (J3) is used to switch between booting to the menu vs booting to a cartridge (Not PB2 which I mistakenly said in the above post). If PB4 is grounded while J9 is still populated (J9 is supposed to be open when booting from a cartridge to disable the Flashback's ROM), it will boot into the ROM's menu code, but the menu isn't rendered correctly because the TIA is attempting to render it instead of Gizmo. Moving the joystick up and down to scroll through the list of games changes the pattern of vertical bars in the bottom third. Pressing fire to select a game causes some random-looking colors to appear in the middle of the screen, but it doesn't actually load a game (probably because Gizmo needs to be active to switch to the correct game address). 

PXL_20240612_040441620.thumb.jpg.5636eece99da18933eb242542a76ebcc.jpg

The colors are the same as what the "Adventure Territory" menu would normally have, which might give some clues to how Gizmo works. According to a comment from Curt Vendel, it's a "super stripped down nes chip", but since the color palette appears to be the same as the TIA, it might be using some sort of hybrid between the TIA and the NES's PPU. For example, it might be using the (likely stripped down) PPU to render the frame and then using some of the TIA hardware to generate the video signal from that. 

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