Jump to content

Photo

Homemade atari super vcs {ntsc} 6502 questions

6502 6507 cy7c408 atari 2600 vcs video computer system TIA television interface adaptor Stella

54 replies to this topic

#51 universal2600 OFFLINE  

universal2600

    Star Raider

  • Topic Starter
  • 85 posts
  • Location:South Carolina, USA

Posted Fri Jun 1, 2018 6:24 PM

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).



#52 universal2600 OFFLINE  

universal2600

    Star Raider

  • Topic Starter
  • 85 posts
  • Location:South Carolina, USA

Posted Thu Jun 21, 2018 5:40 AM

Well I got a 2600 Jr mobo, I've boiled it down to having the 6502 communicate with an atmega644 driving 32k of sram and an ay-3-8910 which also has it's own 16bit gpio for additional expansion, with a few signals taken from other places you could make a small expansion port (well that's the idea) the 644 will hold a small kernel that consists of sound player rountine/gpio handler and accelerated TIA ("ATIA" mode, the 6502 can write the frame to the 644 which can store it in ram, then simply have the 6502 update the parts of the frame that have changed, and whatever hasn't will be free cycles for the 6502 minus keeping sync.

PS: I HAVE A DAY JOB SO I DONT GET PUT MUCH SPARE TIME TO WORK ON THIS, BUT THERE IS PROGRESS..

#53 universal2600 OFFLINE  

universal2600

    Star Raider

  • Topic Starter
  • 85 posts
  • Location:South Carolina, USA

Posted Sat Jun 23, 2018 6:30 PM

Okay I finished socketing this junior mobo, replaced the tia as the co10444d seems to have a better video output vs the um6526, replaced the 6532 aswell, I'm waiting on pin headers for the cpu socket, with the 6502, atmega644, ram and ay-3-8910 connected on a plugin board, (I didn't have a 28pin socket so I just cut a spare 40pin one down)IMG_20180623_202042.jpg


IMG_20180623_202051.jpg

#54 universal2600 OFFLINE  

universal2600

    Star Raider

  • Topic Starter
  • 85 posts
  • Location:South Carolina, USA

Posted Sat Jul 7, 2018 11:56 AM

Okay I have a prototype daughter board in progress, essentially the atmega will handle the ay-3-8910 (32k of ram would be addressed through it's "gpio" with the ram data bus connected straight to the 6502) the pic and 138 are for generating outputs for chip selection (bankswitch), essentially the extra hardware would be outside the normal 6507 memory map, so that any stock 2600 cart could run, but would just allow one to write code for a normal 6502, but also by using the upper address space to use the atmega to do tasks while the CPU is drawing the screen, as well as taking control of the bus, the atmega would have a bootloader that would sit idle until it was addressed directly from the 6502. It simply controls the banks (which the pic and 138 are there for, disabling the Tia, riot,ram,etc)
As well to allow it to play music from the ay38910(combined with the Tia audio, five independent sound channels!) and to halt the CPU and control the Tia if needed

IMG_20180707_115807.jpg

IMG_20180707_115818.jpg

Edited by universal2600, Sat Jul 7, 2018 11:59 AM.


#55 universal2600 OFFLINE  

universal2600

    Star Raider

  • Topic Starter
  • 85 posts
  • Location:South Carolina, USA

Posted Mon Jul 16, 2018 5:40 PM

Finally got the rest of the components (minus a spare 6507), so the board sits snug ontop of a pin header connected directly to the 6507 lines, which would connect to the 6502(no not the one in the picture I have a new one I haven't opened it yet),I plan to use the pic, 138 and gal20v8b (lattice, yes it's obsolete, but it allows one to change the memory map just by flashing a chip😁........and its 5v), as glue logic so I can halt the 6502, generate chip selects, set up in the end you would write to locations that's normally outside the 6507 map, that could represent an instruction to the atmega to set the ram address (using the ay38910 ports) to read or write, and to allow the atmega to drive the tia while halting the cpu,or use the atmega to play sound through the ay38910 (ym player?)
IMG_20180716_191317.jpg





Also tagged with one or more of these keywords: 6502, 6507, cy7c408, atari, 2600, vcs, video computer system, TIA, television interface adaptor, Stella

0 user(s) are browsing this forum

0 members, 0 guests, 0 anonymous users