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Thread: Does the hobby world need another 8-bit kit?

  1. #1
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    Default Does the hobby world need another 8-bit kit?

    I'm considering building up another project soon -- a bus-oriented 8-bit computer. This is sort of an extension of my 8085 SBC project. Having worked with several 8-bit bus architectures, I've naturally come up with what I think would be the "best" way to do it, from a hardware/hobbyist perspective...a combination of the S-100 bus, OSI-48 bus and Apple II bus. Functions would be on separate plugboards with a passive (well, actively terminated) backplane. I'd imagine there would be an 8085 processor board, RAM boards of some capacity, a UART board with boot ROM for monitor, et c.

    While the first processor board would be an 8085-based one, being my favorite 8-bit processor, I'd really like to produce other 8-bit processor boards too. A friend of mine is interested in developing a 6502 board for it, and I'd like to build a NSC800 board as well. The system bus would be designed in a fairly generic manner -- 8-bit bidirectional data, 16-bit address, probably an IO/M control line, reset line, clock line, interrupt line(s)...I'm pretty sure I could fit it into a 50-line bus. To handle the problem of memory-mapped vs. programmed I/O, I have in mind a board that would map part of memory in the top 1K to I/O ports (asserting the IO/M line, et c.). This would allow boards that work with 8085 programmed I/O to be used with a 6502 processor board.

    As to the hobbyist angle, like my 8085 SBC, the boards would be laid out in EAGLE CAD Lite, which is free for hobby use. I know I can pack individual functions onto the 3x4" area limit without too much trouble. The bus connector would be an IDC type, allowing use of cheap connectors for board interconnects (either stacking or backplane).

    Does the world really need me to bother to do this though? The machine will get built anyway, as I want to do this for the learning experience, but I don't know that it's worth the time/money to have boards commercially etched when I can build them with wire-wrap or point-to-point construction. Hobbyists already have a few 8-bit kits to choose from -- the N8VEM SBC being a great example. I want to follow the designs of earlier systems though, mostly through limiting the functionality of each plugboard to a single task.

    So, I guess the question is, does the world need/want another 8-bit kit?

  2. #2

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    Hi! You may want to consider a "standard" bus like ECB. It is not perfect but it would allow you a wider range of options for using legacy boards. The bus control scheme you are describing is well within the ECB standard of 16 bit address, 8 data bits, and all Z80 style control signals (clock, reset, interrupt, etc). The Intel signals are also available on the B-Row. So far, we've placed a Z80, 80C188, and 6809 CPUs on the bus. There is a new host processor in the works too with 6809/6502/6802CPUs with a stand alone ECB

    ECB uses the DIN 41612 96 pin connectors which I consider some of the best and most reliable connectors ever made. They are *much* more reliable than IDC or dual row header connectors. They are cheap, plentiful, nearly indestructible, *and* gas-tight which means they are equivalent to a wire-wrap connection -- super reliable! You could then re-use ECB backplanes and boards. They are fairly common in Europe but less so in the US. You could also use N8VEM boards in your design to help prototype and develop new boards.

    Regardless of whether you start your own system project I wish you the best of luck! It is a lot of fun and I think you'll enjoy it! You are always welcome to use the N8VEM information for your project. I started the N8VEM home brew computing project with helping builders make their own systems as a primary goal but it is certainly not the only way to do it. I hope we can collaborate on some common projects! Please let me know what I can do to help!

    Thanks and have a nice day!

    Andrew Lynch
    Last edited by NobodyIsHere; November 16th, 2010 at 03:32 AM.

  3. #3
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    Sorry for going a bit off-topic, but out of curiosity, how old is the ECB? I found one reference which said the bus was "defined in 1984 by the German company Kontron", but I believe the bus was around many years prior to that? Perhaps there only were 8-bit variants and the first 16-bit addition was made in 1984?

    One member on the (old) VCF IRC today posted scans from Swedish company Scandia Metric who once made a Z80 ECB system called Metric Card. I looked at the pics to determine its age and suggested 1981-82 based on what the broschure says. As this company had a previous history of importing designs, refine and relabel them, I have a feeling one might find some ECB system very similar to theirs, but sold internationally by some other company.
    Anders Carlsson

  4. #4
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    I'd thought about using the ECB, but I think for my project it's a little more than I need...it'd also reduce the available board space in trying to keep the cards within the EAGLE CAD 3x4" limitation. We used to use it at work for some of our control boards because of the high-reliability connections it's known for. Using IDC headers means they're easy to source, and using gold-plated interconnects provides reliable connections.

    I'll probably take a closer look at the N8VEM information in designing these boards, even if just for personal use. It would be nice to have my design be software-compatible, at least to some degree, with the N8VEM ECB (using the same UART, memory map, et c.). I'll probably take a look at your floppy controller design, as I'd like to add one to mine once I get a basic set of boards up and running. The N8VEM ECB is something that's on my to-get list, and has been for a while, anyway!

    There will definitely be community collaboration in what I end up designing...I hope to make something generic enough, and with the right feature set, to enable hobbyists to choose my bus-oriented system for small (modern) embedded projects that would require a more expensive microcontroller or off-the-shelf embedded system. That was the primary reason in designing the 8085 SBC!

  5. #5

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    Hi Anders! Thanks!

    Kontron defined the ECB in the early 1980's but it may well have been in use prior to formal definition. Rolf Harmann in Germany has about the best reference site on ECB I've seen. Rolf has helped me and the N8VEM project many times. He is a great guy!

    http://www.harrmann-rolf.de/

    Also Wolfgang (also from Germany) has a lot of background information on ECB along with a working knowledge of its design and a lot of experience with it. He has a folder on the N8VEM wiki with ECB background information. The meaning of the various ECB signals are a frequent discussion topic on the mailing list.

    Do you have a link to the Scandia Metric scans? I would like to see them.

    Thanks and have a nice day!

    Andrew Lynch

  6. #6

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    Hi! If you want you could use both the ECB and a unique bus and support both types of peripherals. The 8085 to ECB interface is probably going to take about 5 or 6 chips for everything.

    Thanks and have a nice day!

    Andrew Lynch

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  8. #8
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    Going on-topic, it might be nice to see support for the less-known CPUs, but the problem is finding the chips. The National INS8900 periodically shows up on eBay, but not in quantity, for example. SC/MPs are rarer. I have a GI CP1600, but have never run across a Fairchild 9440. The Soviets used a clone of the LSI-11, but those also seem to be hard to come by.

    And that's really a shame--the old chps seem to have gone off to be ground up for their gold content.

  9. #9

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    I haven't seen a 6809/6309 kit out there; that might be nice, as I have a 6309 just sitting around that it'd be fun to put to use.
    Computers: Amiga 1200, DEC VAXStation 4000/60, DEC MicroPDP-11/73
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    "'Legacy code' often differs from its suggested alternative by actually working and scaling." - Bjarne Stroustrup

  10. #10
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    Quote Originally Posted by glitch View Post
    I'd thought about using the ECB, but I think for my project it's a little more than I need...it'd also reduce the available board space in trying to keep the cards within the EAGLE CAD 3x4" limitation.
    I'd sure vote for dual-row headers, cards stacked with spacers and connected with ribbon cable; no card cage, no bus board, cheap, flexible, and if you use the 80-wire 40-pin PATA cable idea you'll even have free 'shields'; you could even have simple transition cards to connect to other buses like ECB or even S-100.

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