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Super atari 6502 (A "DIY" 2600 hardware clone...)

A computer built around a Atari 2600 (VCS), with a few nifty upgrades, 6502, 64k + 128bytes ram, coprocessor, 77 is getting a rework

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Pretty much a 2600 with a full 6502, using the extra address space and Interrupts, along with a Atmega 8515 for bank switching and memory bank management, an atmega 644 (or 8515) as an extra coprocessor which will work similar to an antic chip, hopefully compatible with (most) stock 2600 carts, more or less a 2600 if actually designed around a home computer from the era, note this is a prototype once I have the working and finalized it will have a proper PCB made for it...need to find my PCB cleaner too..... Thing still even fits inside the junior although not without trimming some plastic on the cartridge "key"?

I've gotten the core 2600 chipset wired minus sound and video output, I am using a 74ls00 to generate the clock but the hcu04 will work as well, I'm going to use the unpopulated socket as a sort of expansion port (well header), which will be connected to a daughter board with  the  with the 1k of dual port SRAM which I want to use to implement part of a  line/frame  buffer, and 32k of general sram, and 32k of video and audio ram, and 256k flash.

The cartridge can be used to simply bank into the 256k ROM which can hold an OS and/or subroutines/kernels for sound and video, custom graphics/sound data, games, etc..., from there you can bank between the IO (TIA/RIOT) and memory (Cartridge/32k ram/ 256k flash), essentially I have a 2600  with a full 16-bit address bus, plus interrupts and 2-phase clock output, the socket is where  a daughter board (I ran out of space) which holds the glue logic, 32k RAM ( TBH  I am leaning towards using the internal ram of the MCU instead of the dual port simply for space), and 256k of flash.

  • 1 × R6532P Microprocessors, Microcontrollers, DSPs / IO Controllers
  • 1 × R6502BP Microprocessors, Microcontrollers, DSPs / Microprocessors (MPUs)
  • 2 × atmega8515 (or 644) Microprocessors, Microcontrollers, DSPs / ARM, RISC-Based Microcontrollers
  • 1 × CO10444D-11 Tsu branded 2600 graphics processor
  • 1 × IDT7130LA Memory ICs / Static RAM (SRAM)

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  • update 08/19/2018

    Robert08/19/2018 at 11:59 0 comments

    still working on this, i've boiled it down to using a vcs junior motherboard with the 6507 removed and socketed a header to a daugherboard with a 6502, GI  ay-3-8910, 32k ram, and atmega644 and a gal20v8 and some 74 logic (for internal bankswitching), i work 10 hours a day, so spare time is limited, im still working on this, i will have pics soon

  • Delays.....but still making progress

    Robert06/10/2018 at 21:46 0 comments

    okay, I ended up having to refund my money for the sram, since it never arrived, but I was able to instead buy 128k worth of sram in a lot of 4 separate 32K chips for the same price, im using two of them one for normal program/data ram to extend from the 128bytes, which the atmega8515 will act as a mmu to read from and write to ram using the upper address bits to access either the mmu or the the dual port ram (IDT7130SA55) which would act as a memory buffer, though i am considering using atmega644 instead of an 8515 for its extra memory, only difference is no port E and but much more memory versus the 8515, but the 6502 would write to the ram, which the atmega would either do nothing, store it, or load it and do some processing, and store back to the dual port ram or store in in its own 32k for later use or vice versa. also i would use the atmega to control the tia and 6502, using the 6502 itself, i.e having the 6502 trigger the atmega which would halt the 6502 using its rdy line, and assume control of the tia, thing is either you can use the 6502 for addressing the tia, but would be limited to the 1.19 mhz clock (both atmega chips will run @ 21.47727MHZ) , or  instead use atmega to handle the tia bus, but the way i would implement this i think most likely would break normal 2600 compatibility unfortunately.

    TL;DR

    i had reorder sram but got a better deal , i've gotten some dual port ram, current progress is getting the memory map structured properly so that if you plug in a 2600 cart it will run just fine, but you insert a cartridge with homebrew code that would read and write to the extra address space, then you can use the extra hardware added to the system and use the 32k of ram and the dual port ram which the display co-processor would sit behind with its own 32k of video or  just general purpose ram (ie you could store graphics or program data or both if you wanted to).

  • updates

    Robert05/13/2018 at 23:19 0 comments

    ive decided to drop the 32 bit mcu atm becuase it doesn't have a full (8bit) io port,  using two atmega 8515 @ 6 times the tia clock (21.47727 mhz) one used as a gameboy like MBC (you can bankswitch[32k ram/flash/gpio etc] and by writing to the data bus, using the upper address bits of the 6502, could be used as a co-processor aswell imho) , the other soley used to drive the TIA, with it having its own 32k of  "display" ram,  and would be accessed also with the extra address bits from the 6502, this chip will function similar to an antic cpu, to offset the display to the atmega, and do your logic with the 6502 cpu

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adam.klotblixt wrote 04/25/2018 at 06:56 point

A promising project. Would appreciate some more details in due time.

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Robert wrote 05/04/2018 at 22:44 point

thanks, progress is a bit moderate, mainly due to my desktop mobo hitting the shitter, working on resolving that, on top of waiting on a few more parts (dual port ram and sram) that snail mail "express" is currently delivering...

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