6502.org

Hi there,

I would like to introduce you to our (me and a friend of mine) little homebrew computer project called "Steckschwein".
At the moment, the computer only exists on a breadboard (german: "Steckbrett"), which can be a pig (german: "Schwein") sometimes, hence the name.

The Steckschwein began existence quite exact a year ago as a series of experiments with a 65c02 on a breadboard.
What started as a slowly (~500Hz) clocked something with the address bus hard wired to $EA (NOP) and a bunch of LEDs attached to the address bus evolved quickly into something resembling a full blown computer.
We then used Chris Ward's computer from the homebrew project page as a place to start, and started to change (maybe improving) things, so now there is not much left from Chris's design anymore.
After realizing that we really might pull it off to design our own retro computer, we made it our ultimate goal to build a computer that could have existed in the good old times, but with more modern interfaces and means of bulk storage. So we did not even consider using some IDE or whatever hard drive or even a floppy disk drive and went straight for an SD-Card instead. Also, PS/2 keyboards are both modern and retro, so we would go for that.
We started with the notorious 65c51 for implementing a serial interface, but switched to a 16550 UART pretty soon.

Today, the Steckschwein evolved into a (two to be exact) big mess on a breadboard with the following specs:

• - 65c02 @ 4MHz
  - UART 16550
  - TMS9929 Video Display Processor
  - 64k SRAM
  - 8k ROM (8k window selectable from 32k ), can be switched off to make the ram underneath accessible a la C64
  - 65c22 VIA used as an SPI master, bit banged. Attached via SPI:
  • - DS1306 RTC
    - ATmega8 used as PS/2 keyboard controller
    - SD-Card

We have set up a (very terse, also german) project website at http://www.steckschwein.de and we try to blog stuff at http://8bit-gefriemel.blogspot.de/ . Also in german, but there are pictures, too.

So, that's what we did, hope you enjoy it, and don't hold back on any feedback.

Cheers,
ArnoldLayne

Welcome! Always good to see a new single-board (or breadboard) adventure. Will follow with interest!

Thanks for publishing your code: I see Wozmon, Forth, and a 3d-demo. And a plan to run the C64 Kernal?

Cheers
Ed

Hello, and a warm “Willkommen” to the 6502 forum.

Gotta a kick out of the name. Welcome!

Yes, thats a bunch of things we've been playing around with. We might do a port of one or another thing, and I am also dreaming of doing a full blown operating system (SteckOS), but one thing after another. First we need proper PCBs.

Everything we code will end up in our repository on SourceForge, even the embarrassing stuff.

Bedankt!

Takes two to know!

Very nice project! You should post on the "Introduce yourself" thread, under General Discussions.

Regarding SPI, you will find a nice alternative to bitbanging on a 6522 is to use Daryl Rictor's 65SPI device. It requires a Xilinx XC9572 CPLD, but will be a lovely addition to your computer.

More info on this post: viewtopic.php?t=1265

A really lovely little computer you've built there! Are you planning to make the PCB yourself, or get one made up "professionally"?

Welcome to our Schweinestall!

I'm curious about the RTC selection. Any reason you didn't go with the DS1643, which would offer 8kb NV RAM instead of those few bytes? (http://www.maximintegrated.com/en/datas ... vp/id/2743)

Hey! My office doesn't resemble a pig sty...not usually...er, most of the time...

Right, that thing (also Andre Fachats modified version) is very tempting and might be used in one of the next iterations of the steckschwein. I first have to get started with all the FPGA/CPLD-stuff.
First, we will do boards of every "subsystem", that is, CPU/memory, IO, UART, Video, and connect them with a SCSI cable as an el cheapo backplane.
At some point, as soon as we find the Steckschwein has everything we think it should have, and works the way we intend it to work, there will be a single board version.
We will do the layouts using KiCad and have them manufactured.

Hehe, yeah!
Yes, as a design decision I wanted to go with the SPI bus for that kind of stuff. So I was only looking for RTCs with SPI interface. A friend of mine suggested the NXP PCF2123 and the Maxim DS1306. The latter comes in DIP package and Maxim was kind enough to send me samples, so that's that.
I am also quite happy with 96bytes NV RAM, since I'm only planning to store config settings there.

FYI, jesari has a great little circuit which, by using the shift register, supercharges a VIA's ability to manage SPI. It's not quite as fast as Daryl/Andre's approach, but it takes minimal hardware and thus offers excellent (bit)bang for the buck. viewtopic.php?f=4&t=1674

Yes, I remember stumbling upon this when doing research for SPI, which was totally new to me at that time. This really looks worth trying. No Idea why I did not consider this back then. Unfortunately, the link to the schematics seems to be dead.

If this can't be resolved then I'll upload the schematic myself. I'm out of town right now but have a copy on my machine at home.

Personally I find the VIA-SPI idea very appealing. It`s just a small amount of hardware, judiciously applied, and it solves the only problem not soluble by software -- namely, the bottleneck on transmission of the datastream itself.

-- Jeff