Well here I go reviving this everlasting thread once again, but that is how my project is going as well!
After a few years of experimentation I finally have what I am calling my "final design". The Lazarus-64 Retro Game System is getting one last full bread-boarding and then all of the details are being posted here...
I am hoping that those interested in video generation and interfacing AVRs to external SRAM will find this project interesting and one day hope to amass a large collection of games, demos and utilities for the system.
The final specifications are as follows...
- Video is composite NTSC 224x200 with 256 colors. the signal is very close to spec and will work on any TV or monitor with a composite input.
- Sound is 4 voices with multiple waveforms and envelopes. Output is a standard mono line out.
- Memory is dual 64K buffers with a blazing 14MHz bandwidth directly to the host processor. Since a 20MHz AVR can only hope for 10MHz in assembly, this is pretty fast, and there are absolutely no timing constraints when writing to the video memory as the Lazarus video switcher makes it seem like a standard 64K SRAM using 16 address bits, 8 data bits, OE and WE. Double buffering is fully transparent.
This system is truly retro because all parts were available in 1980, and it connects to any processor or microprocessor. AVR, PIC, ARM, CPLD, FPGA, or even a 6502 at 1MHz if you wanted.
The host microprocessor can be running at any clock speed from 1MHz to 32MHz and any language can be used, so this system is truly universal.
Well, enough talk... I have to actually document the thing now and hope to have the site completed in a few more months. Schematics, sources codes, parts list, and many examples to come!
Once again, thanks to all freaks and the owner of this great site as I made my first steps here and found this place to be the ultimate AVR resource!
I Like to Build Stuff : http://www.AtomicZombie.com
Thanks! I will post each time I make a useful update since I am actually planning to finish this project now.
Just found the perfect set of chroma taps...
Hi! This is great! I think it would make for a very nice ECB board for the N8VEM home brew computer. I am anxiously looking forward to your completed design. Are you planning on posting your design as free/open source or commercial?
Thanks and have a nice day!
PS we are testing the N8VEM SCG (sprite & color graphics) board. It has a TMS9918 for sprites and color graphics and an AY-3-8910 sound chip for effects. Things are coming along and I am looking forward to some neat demos. There is a "space invaders" type demo game in development and there is a video on the N8VEM wiki.
Everything is going to be open source and open hardware. If there is enough interest, I plan on making 100 boards and will sell them at cost, although I really hope most will just perf-board the design... that keeps it fun!
All sources for the sync generator and multi-voice sound system will be available for download as source or hex files and I will eventually make them for both PIC and AVR.
Also planning on doing all major arcade game conversions as well as some original designs in assembly, basic, and for AVR and PIC just to help everyone get started. Since Lazarus can connect to any 32 IO microprocessor/microcontroller, I will probably dig into ARM and XMos as well.
The idea is to create the ultimate site jammed with info on using microcontrollers and old-school logic to make retro games or just learn about video generation.
Since this design cannot become obsolete, I hope to maintain it for both my own enjoyment as well as others for decades to come. When I say "cannot become obsolete", I mean that there is not one single hard to source or custom IC used, just common 10 cent logic and a few 32K SRAM chips. No specialty video ICs to go obsolete, no single source parts, and no parts that have to be dug out of a cellar full of cold war-era mainboards! I can't see we the entire design will not be just as useful in 40 years from now.
The current site is just a sloppy build log as I make the solderless breadboard version for the 5th time to iron out the last few bugs. I will then hand wire another (3rd) full breadboard version, do some quality tests and then commit the design to a schematic complete with step by step build instructions, alternate parts lists and explanations on how every single part of each sub-circuit works.
After that, I will make a PCB and offer it up to those with soldering iron phobia and to help pay for bandwidth costs!
I only do this stuff a few hours per week, but it will all come together fairly soon now.
Sounds good. Put me on the waiting list for a couple of the boards when they're ready.
"I wish I were dumber so I could be more certain about my opinions. It looks fun." -- Scott Adams
Did you see this?
Apparently, you can use one of the new "quad-wide" SPI RAM chips in "Burst Mode" to punch out 4bits at a time given only a clock input (at up to 20MHz.) That sounds pretty ideal for generating multi-bit video from any microcontroller with a timer output, and simultaneously solves (somewhat) the RAM problem. A suitable 64kbyte RAM chip is less than $2 in small quantities.
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