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Thread: z80 and hardware

  1. #1

    Thumbs up z80 and hardware

    ok, so what i want to ask is i'm not a EE guru. i have a little knowledge but not enough to design and make a pc from scratch. what i want is to play around with some z80 bases systems i have and try some ideas in interfacing things to them.. but i have no idea where to start. i have been looking over the net for the last week and it is so confusing to know whats whats. and a lot is for either a make of system or the s100 systems.. and a lot don't have schematics so i can try to understand. so can anyone recommend a site of tutorial on such things??? i am up to trying out things so long as i have some guidance help with what does what and why/how ..

    thanks

  2. #2

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    I have a history with Heathkit/Zenith computers and so have been a member of the sebhc google group. But one site of particular interest is http://koyado.com/Heathkit/. Norberto has been lead/catalyst on a lot of new boards. He's got a new Z80 board that is pretty much stand-alone (some upcoming additions make it completely stand-alone), and you can also build the H8 backplane (sideplane) and create a modern H8. He's also got an H89 variant as well. Architecturally, these are "antique" computers but they have many modern features and enhancements. In the wings are GIDE and WIZNET add-ons giving you direct access to IDE/CompactFlash and Ethernet.

    It really depends on what you want to do. I have provided software development for some sebhc projects, but I own no real hardware. I run a series of emulations and simulations in order to provide software that has final testing done on real hardware. There are lots of emulators/simulators out there to choose from. If you are interested in what I've been using, let me know.
    - Doug

  3. #3
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    If you want a basic starting point, try one of the Z80 kit computers that are currently around. Something like the RC2014. You can pick up everything you need from the guy who makes them (he sells them on Tindie) and there's a lot of other people hacking on them, so if you hit a snag it shouldn't be too hard to find help. You can run CP/M off a CompactFlash card, which is way easier and more reliable than getting a floppy system going. There are also single-board Z80 systems which is of course everything on one card, like Sergey's Zeta SBC. That has the benefit of being even simpler to assemble, but expansion is limited.

  4. #4

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    You need to start by looking at the timing diagrams for the Z80. You need to understand what is different about each diagram (read, write, I/O, interrupt and DRAM refresh). You can the decide how your circuit might combine the signals to decode unique operations for the various operation. If you plan on using static RAM, you can ignore the DRAM. Look at each diagram and make note of what is in common and what make each unique. Also, make note of when your circuit is playing part in the timing and when the processor is on its own.
    Pay especial note as to the differences between and interrupt, I/O or memory operation. Your circuit must include all the differences in these conditions to avoid corrupting the other operations that look similar. You don't want an intended memory write to also cause a write to an I/O port with the same data. The hardware you design must protect against such things.
    Look on bitsavers.org for Zilog data manuals that describe the Z80. Also, try to get data manuals for any part, RAM, I/O chip and such, that you intend to add to your system. You want to see how the Z80 timing diagram can provide the needed signal to match the periphery components timing diagram.
    Making systems is all about matching up these timing diagrams.
    You also need to understand logic. For the most part, you'll be using NANDs, NORs and D-Fipflops. You might also use XORs or comparitors for such things as address decoders. Familiarize yourself with how these circuit work. Look at truth tables until you can understand what they are for.
    One last thing. Every logic operation takes some time. For most things, one can run the main clock slower to compensate for these delays. This is true for most things but things like DRAM have maximum delays for things like refresh. Although, it is easier to get big DRAM than static I recommend staying with SRAM until you are willing to do thorough timing analysis of your circuits.
    You get all that and you'll be a designer.
    Dwight

  5. #5

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    http://searle.hostei.com/grant/cpm/index.html

    A 9 chip Z80 CP/M computer you can build yourself. Might be interesting to try it. Much cheaper than building from a kit.

    I do second what Dwight has said although I sometimes find timing diagrams tricky to follow. That hasn't stopped me from learning though (and designing / building hardware of my own).

  6. #6

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    FYI, no floppies are required with the Heathkit hardware, although I doubt that is what you are looking for. I mention it because the H8 system bus is fairly well defined and has a long track record. It's by no means perfect, or perhaps even good, but it does work. S100 also has a long track record, but did have some problems at times - perhaps related to using cheap connectors.

    I think there are probably enough people on this forum that have experience interfacing to the Z80 that you can get help. Probably just a matter of you making a choice on what platform to use. You have some good suggestions to start from.
    - Doug

  7. #7

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    thanks everyone i will take on board what has been said and make up my mind.. and thanks again

    p.s. i'm looking at an existing system with z80 that i want to add to.. so will see what i come up with..

  8. #8

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    You can build a Z80 SBC without glue logic with RAM, EPROM, Z80 and SIO. It can support CPM2 with Compact flash interface and two common TTL logic. The design files are here: https://retrobrewcomputers.org/doku....lasmo:simple80. You can purchase the Simple80 IC kit from this eBay vendor for $6 plus $6 shipping. https://www.ebay.com/itm/Simple80-Z8...t/113735638336

    I will soon publish rev1 of Simple80 where CF interface is integrated on the motherboard so the 3 RC2014 expansion slots remain uncommitted. The goal is a Z80 SBC with expansion and CPM capabilities where an inexpensive & proven kit is available. I like to keep the part cost down to $20.
    Bill

  9. #9
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    Quote Originally Posted by JonB View Post
    http://searle.hostei.com/grant/cpm/index.html

    A 9 chip Z80 CP/M computer you can build yourself. Might be interesting to try it. Much cheaper than building from a kit.
    It has long been on my list to get around to banging out one of Searle's computer-on-a-breadboard designs. They look like a great place to start if you want to try building something completely from scratch and the fact that he has ROM/filesystem images already prepared for them is a major plus.

  10. #10
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    Quote Originally Posted by Plasmo View Post
    You can build a Z80 SBC without glue logic with RAM, EPROM, Z80 and SIO. It can support CPM2 with Compact flash interface and two common TTL logic. The design files are here: https://retrobrewcomputers.org/doku....lasmo:simple80. You can purchase the Simple80 IC kit from this eBay vendor for $6 plus $6 shipping. https://www.ebay.com/itm/Simple80-Z8...t/113735638336

    I will soon publish rev1 of Simple80 where CF interface is integrated on the motherboard so the 3 RC2014 expansion slots remain uncommitted. The goal is a Z80 SBC with expansion and CPM capabilities where an inexpensive & proven kit is available. I like to keep the part cost down to $20.
    Bill
    Neat project! I'm hoping to get the same type of thing going with Glitchbus, but haven't gotten enough of it nailed down yet

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