Home built Z80 computers - CP/M

This is a discussion on Home built Z80 computers - CP/M ; Lee Hart wrote: > I'd be happy to share the design for my Databug. It was designed for > a data logger, but could run CP/M using the memory above 64k as its > disk. Not exactly traditional, but very ...

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Thread: Home built Z80 computers

  1. Re: Home built Z80 computers

    Lee Hart wrote:
    > I'd be happy to share the design for my Databug. It was designed for
    > a data logger, but could run CP/M using the memory above 64k as its
    > disk. Not exactly traditional, but very cheap (all the parts cost
    > under $20).
    > - 6.5" x 2.5" PC board
    > - Z80
    > - 2 bytewide memory sockets, up to 1meg memory, bank switching logic
    > - two serial ports (one RS-232, one special)
    > - 3-channel A/D converter
    > - switchmode power supply.


    pbetti wrote:
    > Sounds like a very nice design. If you could really share the project
    > (at least) i'm interested.


    I don't have a website, but would be happy to post the schematic or
    board layout. Anyone have any suggestions on where to put them?

    But the Databug is a specialized solution, intended for another purpose,
    but that can be "pressed into service" for CP/M. There are of course
    hundreds of Z80 systems already for which the same could be said. People
    will always pick the one they already happen to know, or have, or can
    get cheap.

    I think if the goal is to home build your own computer, then the design
    has to be *suitable* to be home built. That means it should avoid parts
    that are expensive or hard to get. It should avoid assembly difficulties
    like surface mount or tight spacings. It should be well documented. And
    lots of people should have "passed that way before", so you can follow
    in their footsteps, rather than have to re-invent everything yourself.

    I've been thinking about doing this for a long time, and have discussed
    some ideas on this newsgroup. I thought about recreating the Altair
    8800, but it has too many parts and is basically not a very good design.
    I looked at the IMSAI 8080, which is a better design; but there are
    still lots of expensive parts (100-pin edge connectors, expensive
    switches). Plus, it's already being done.

    So, my current thought is to recreate something like the Heathkit H8. It
    was designed to be built as a kit, and so is particularly easy to build.
    It came with the legendary Heath quality manuals, written so *anyone*
    could build it. In its basic form, you got a 2 MHz 8080 CPU card with 1k
    monitor ROM, 8k RAM card, and front panel card with keypad and 7-segment
    LEDs. The cards were large; 6"x12", with all chips socketed and very
    large spacings and pads for easy soldering. The cards use pin-and-socket
    connectors (Molex KK series; 0.025" square pins on 0.1" centers) to plug
    into a 10-slot motherboard with a 50-pin bus.

    There were *lots* of accessory cards to add the Z80 CPU, memory, serial
    and parallel ports, cassette and disk controllers, color/graphics,
    sound, etc. Being home built, and since Heath provided full schematics,
    board layouts, source code listings, etc. lots of people built their own
    boards.

    Several disk operating systems were used; CP/M (several versions), HDOS
    (Heath Disk Operating System), FORTH, UCSD Pascal P-System, etc. The H8
    was highly compatible with the Heath H89 and Z-100 (running on the
    8085); most software worked the same on all of them.

    The H8 cabinet was much simpler than most S-100 boxes, and can easily be
    built with flat aluminum sheets and simple tools. It had a linear power
    supply and no fan (convection cooled).

    I think we could build a "clone" of the H8 that is fully compatible
    software-wise, but uses more modern parts to simplify construction and
    reduce cost. Modern 74HC chips reduce power and noise, and it takes
    fewer of them to perform the same functions (octals instead of quads,
    etc.) The entire 64k memory is now a single CMOS bytewide chip, rather
    than dozens of 4k chips.

    The greatly reduced chip count would allow smaller boards -- this gets
    the price down considerably. The "motherboard" could be just a ribbon
    cable with the desired number of IDC connectors crimped onto it.

    Rather than the now-rare Molex KK bus connectors, use 25-pin D
    connectors for the bus; they are common, reliable, and mechanically
    rugged.

    I'm not sure what to do about the disk controllers, though. The Heath
    designs used Western Digital chips, which are now hard to get and not
    very sensible for a new design. But if something else is used, (765?),
    then all the hardware has to be redesigned and all the software
    rewritten.

    Any thoughts?
    --
    Ring the bells that still can ring
    Forget the perfect offering
    There is a crack in everything
    That's how the light gets in -- Leonard Cohen
    --
    Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

  2. Re: Home built Z80 computers

    ziggy wrote:
    > Personally i dont think 'cloning' anything is the right idea, it should
    > be something unique, designed from scratch.


    If you start from scratch, then it's a lot more work to ever reach even
    a modest level of functionality. It would be likely to become a project
    that never gets finished.

    > I also agree that we will have to make some concessions for the loss of
    > 'classic' components over the years, but i would think we should get by
    > with a bare minimum of 'modern' parts in this thing.


    I agree. Though it is tempting to use "new improved" parts, in may cases
    they are also single-sourced and availability is poor. Probably 9 out of
    10 new ICs won't survive; their manufacturers will soon give up and drop
    them.

    I tend to stick with generic multiple-sourced parts that have been
    around for 10 years or so. Once they have a broad user base, they tend
    to *stay* around much longer. So the odds are good that I will still be
    able to get a replacment part 10 years in the future.
    --
    Ring the bells that still can ring
    Forget the perfect offering
    There is a crack in everything
    That's how the light gets in -- Leonard Cohen
    --
    Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net

  3. Re: Home built Z80 computers

    >I don't have a website, but would be happy to post the schematic or
    >board layout. Anyone have any suggestions on where to put them?


    I can offer either/both my yahoo and comcast personal websites.

    yahoo :
    pros: that site has been around for awhile, and will likely remain
    that way.
    cons : heavy advertising.

    comcast :
    pros: Less advertising, the site is (for the moment) 'cleaner'
    (as in less cluttered), easy file management (for me!)
    cons: It's dependant on my Dad's comcast account. If he
    gets a twist in his shorts and cancels his subscription, I
    lose my sub-account.

    My thoughts about the project in general:

    While I would love to dive into an ASIC project, I also
    love simplicity, commonality, and ease-of-replacement:
    If I release the magic smoke on an ASIC, I'm gonna
    be pretty mad. If I smoke a Z80 or '138, I can get over it
    much easier and faster.

    A lot of machines were built without an ASIC- Kaypros,
    the H8, and many others. Lot's of homebrewers out there
    manage quite nicely without them as well.

    I'm all for using a pre-existing design for a starting point;
    but I don't wan't to shy away from rewriting
    (maybe even large) portions of the code, if it will serve
    our purposes- such as the idea of upgrading the H8's
    1701 (? WD) in favor of the 765. As an aside, I have a
    765A, and was wondering when I'd get around to using it.

    I propose setting some 'baselines' - issues we can agree
    on now - to get the ball rolling.

    proposals -
    Z80 @ 4MHz : is there a reason to be slower or faster?
    Disk Controller: 765A (cuz I have one ;o) )
    True I/O : as opposed to memory-mapped. [1]
    Rsvd Ports : for options like color/grafix/sound [2]
    CP/M : (was there ever any doubt?) 2.2 for simplicity?
    Drives: 3.5" cuz they're thick in these parts.

    [1] This is a wonderful feature of the Z80, that requires
    only two to four gates to implement. And I am a byte
    hog; the thought of sacrificing RAM addy's for hardware
    just makes me itch.

    [2] In this way I am kind of signaling that I am leaning
    towards a tty design. But I like the thought of leaving
    'room' for people to extend the base design in their own
    way- implement their own customized peripherals and
    the code to use them.

    After writing all of this, I just realized the H8 was an 8080
    based design. Which actually doesn't affect much as far as
    my proposals are concerned, I don't think. The 8080 only has
    512 I/O ports, which is still probably more than I'll *ever* use,
    but the Z80 did some cool things with diffferent out(~~) instr's.
    I guess the both biphase clock and the bivoltage supply of the 8080
    scare me.

    Lemme know whatcha think.

    -Tarkin


  4. Re: Home built Z80 computers

    On 15 Apr 2006 20:37:52 -0700, "Tarkin" wrote:

    >serve
    >our purposes- such as the idea of upgrading the H8's
    >1701 (? WD) in favor of the 765


    Upgrading? Who (or what) are you people, anyway?

    Bill

    who:

    1-bought one of first Xerox 820s ever sold (1981)
    2-discovered its many many limitations
    3-found designer, called him, learned about Bigboards
    4-built two BB IIs, one for friend, one for myself (1982)
    5-used BB II extensively for several years

    There is no better Z-80 implementation anywhere
    than the BB II. It has all the support chips: the CTC chip;
    the DMA chip; the PIO chip; the full blown SIO chip,
    and is the classic 'everything in the Intel databook
    implementation' with the addition of a SASI interface
    and the ability to program it's own BIOS ROMs.

    You need either a keyboard and a monitor OR a
    serial terminal (or a computer that looks like one)

    And, of course, what ever kind of storage you can
    wire up - drives, tape, paper tape, whatever.

    It has an extensive built-in monitor that does
    almost everything but write programs for you.
    Which includes, INing and OUTing whatever
    bits it takes to get all your I/O working right.

    You don't even need an operating system to
    save and get bits from your storage device(s).

    Meaning: you can start from SCRATCH and
    work up your boot interface, then paste it
    onto ANY Z-80 operating system image, from
    any device you can read from, and then
    save it out to ANY storage device you have.

    If you don't have ANY, then burn yourself
    a ROM of the thing. It's even got extra
    sockets to stash hardprogrammed code.

    They didn't leave anything out. Period.

    Because of it's hardware interface capabilities
    there is NO WAY you can do it all with ANY
    emulator. The BB II is/was uniquely versatile.

    Call it the pinnacle of Z-80 development systems.

    (and, it is impossible to emulate the 1791/3 type
    disk controller with a 765. IT CAN NOT BE DONE.)
    IBM and the others chose the 765 at least in part
    because of it's 'ability' to protect THEM and their
    precious softwares from unauthorized copying.
    Which included, making safety backups yourself.

    With the 1793 you can copy ANYTHING, with the
    only exception being those little laser holes. For
    some reason they forgot to give it a turn-on-the-
    laser output port. Probably so you wouldn't
    accidentally burn up your disks. Anyway, not too
    many disk drives came with them (hole burners).

    And, maybe 'weak' bits. Not too sure about them.


  5. Re: Home built Z80 computers (oops)

    On Sun, 16 Apr 2006 09:57:35 -0500, wild bill
    wrote:
    >
    >There is no better Z-80 implementation anywhere
    >than the BB II. It has all the support chips: the CTC chip;
    >the DMA chip; the PIO chip; the full blown SIO chip,
    >and is the classic 'everything in the Intel databook
    >implementation' with the addition of a SASI interface
    >and the ability to program it's own BIOS ROMs.
    >


    Well, okay, so try Zilog Databook.

    Ever since, it's been Intel On My Mind.

    With an occasional AMD breeze.....

    Bill


  6. Re: Home built Z80 computers

    On Sun, 16 Apr 2006 09:57:35 -0500, wild bill
    wrote:

    >On 15 Apr 2006 20:37:52 -0700, "Tarkin" wrote:
    >
    >>serve
    >>our purposes- such as the idea of upgrading the H8's
    >>1701 (? WD) in favor of the 765

    >
    >Upgrading? Who (or what) are you people, anyway?
    >
    >Bill
    >
    >who:
    >
    >1-bought one of first Xerox 820s ever sold (1981)
    >2-discovered its many many limitations
    >3-found designer, called him, learned about Bigboards
    >4-built two BB IIs, one for friend, one for myself (1982)
    >5-used BB II extensively for several years
    >
    >There is no better Z-80 implementation anywhere
    >than the BB II. It has all the support chips: the CTC chip;
    >the DMA chip; the PIO chip; the full blown SIO chip,
    >and is the classic 'everything in the Intel databook
    >implementation' with the addition of a SASI interface
    >and the ability to program it's own BIOS ROMs.
    >
    >You need either a keyboard and a monitor OR a
    >serial terminal (or a computer that looks like one)


    H8 has a software driven front pannel.

    >And, of course, what ever kind of storage you can
    >wire up - drives, tape, paper tape, whatever.


    H8 had disk, paper tape and even cassette.

    >It has an extensive built-in monitor that does
    >almost everything but write programs for you.
    >Which includes, INing and OUTing whatever
    >bits it takes to get all your I/O working right.
    >
    >You don't even need an operating system to
    >save and get bits from your storage device(s).
    >
    >Meaning: you can start from SCRATCH and
    >work up your boot interface, then paste it
    >onto ANY Z-80 operating system image, from
    >any device you can read from, and then
    >save it out to ANY storage device you have.
    >
    >If you don't have ANY, then burn yourself
    >a ROM of the thing. It's even got extra
    >sockets to stash hardprogrammed code.
    >
    >They didn't leave anything out. Period.


    Sounds like SB180, AmproLB+, Davige
    and a raft of others.

    >Because of it's hardware interface capabilities
    >there is NO WAY you can do it all with ANY
    >emulator. The BB II is/was uniquely versatile.
    >
    >Call it the pinnacle of Z-80 development systems.


    You forget many others out there.

    >(and, it is impossible to emulate the 1791/3 type
    >disk controller with a 765. IT CAN NOT BE DONE.)


    Why would you.

    >IBM and the others chose the 765 at least in part
    >because of it's 'ability' to protect THEM and their
    >precious softwares from unauthorized copying.
    >Which included, making safety backups yourself.


    Bogus and meaningless.

    >With the 1793 you can copy ANYTHING, with the
    >only exception being those little laser holes. For
    >some reason they forgot to give it a turn-on-the-
    >laser output port. Probably so you wouldn't
    >accidentally burn up your disks. Anyway, not too
    >many disk drives came with them (hole burners).


    Not quite but, their extinct anyway.

    >And, maybe 'weak' bits. Not too sure about them.


    ??

    Allison

  7. Re: Home built Z80 computers

    In article <1145158672.790102.135200@u72g2000cwu.googlegroups. com>,
    "Tarkin" wrote:

    > >I don't have a website, but would be happy to post the schematic or
    > >board layout. Anyone have any suggestions on where to put them?

    >
    > I can offer either/both my yahoo and comcast personal websites.
    >
    > yahoo :
    > pros: that site has been around for awhile, and will likely remain
    > that way.
    > cons : heavy advertising.
    >
    > comcast :
    > pros: Less advertising, the site is (for the moment) 'cleaner'
    > (as in less cluttered), easy file management (for me!)
    > cons: It's dependant on my Dad's comcast account. If he
    > gets a twist in his shorts and cancels his subscription, I
    > lose my sub-account.
    >
    > My thoughts about the project in general:
    >
    > While I would love to dive into an ASIC project, I also
    > love simplicity, commonality, and ease-of-replacement:
    > If I release the magic smoke on an ASIC, I'm gonna
    > be pretty mad. If I smoke a Z80 or '138, I can get over it
    > much easier and faster.
    >


    A fpga is really tempting me as well, for about 150 bucks and i have
    plenty of hardware to do most any z80 project ( or 6502, etc ) i want,
    and if i is crew it up, just erase it and start over.

    But, that sort of takes away from the whole retro idea and wouldnt be as
    much fun..

  8. Re: Home built Z80 computers

    >But, that sort of takes away from the whole retro
    >idea and wouldnt be as much fun.


    I wholeheartedly agree. I was tempted, as
    well, after looking at the Spartan3 dev
    board from http://digilent.com .

    I have a decent machine running CRUX linux
    2.0 (eveolution), w/ gcc 3.4, and all sorts o'
    libxxx's; I also have the J2SE sdks for win
    and linux; but I get my kicks from writing
    'Hello world!' using cp/m, MAC, and ED.
    (My main box, the one I usually compose
    my thoughts to the groups on, is a WinXP box)

    I am not entirely against the idea of using the BBII
    as starting point, either; I've heard good things
    about it before.

    I am also totally for using modern equivalents
    of some of the componenets from yesteryear:
    one of the prev. posters mentioned octal vs.
    quad latches (registers? something), and his
    point about the lower power consumption of
    the HC devices is spot on; I don't believe
    that these enhancements will violate the
    spirit of the OP's project idea.

    I guess the idea of using an fpga suggests
    (to me) using a more robust fpga, and
    implementing all of it on a single chip, or
    use an fpga + 2/3 support chips, and do
    it all surface mount on a credit-card sized
    card.

    My interpretation of the OP's intent for the
    proj was something that would use cheap,
    readily-available components, easily assembled,
    and that the design would be something a
    reasonably bright 10-12 year-old could
    assemble, grabbing an elder for assistance
    w/ the programming & firmware.

    TTFN,
    Tarkin


  9. Re: Home built Z80 computers


    Tarkin wrote:
    > >But, that sort of takes away from the whole retro
    > >idea and wouldnt be as much fun.

    >
    > I wholeheartedly agree. I was tempted, as
    > well, after looking at the Spartan3 dev
    > board from http://digilent.com .
    >
    > < sniped >
    >
    > TTFN,
    > Tarkin


    This is just another bunch of random ramblings on my part so take what
    you want and leave what you don't want. :-)

    I was thinking of sticking to the standard Z80 and its support chips,
    WD279x FDC and the GIDE interface. All of the "glue logic" would be
    implemented in a couple of CPLD (Atmel or Xilinx). The parts are not
    that expensive, $6 to $12 each, and don't require any special
    programming hardware. The parts are in system programmable through the
    JTAG port. The development tools are free.

    Don


  10. Re: Home built Z80 computers

    In article <1144973073.754320.312890@i39g2000cwa.googlegroups. com>,
    "Don" wrote:

    > Tarkin wrote:
    > > Thanks for the tip. I realized the bit about the
    > > registers initializtion being specific to operating
    > > parameters and port mode, but it's gotchas
    > > like keeping a copy of the xmt status that I
    > > suspected would cause hours of r&d and
    > > forensic debugging.
    > >
    > > I am off to hunt down the AMD spec/docs.
    > >
    > > To birng us back on track, what's the consensus
    > > on a z80-based homebrew? Book? Databug?
    > > Shameless eastern-bloc rip-off of the p112?
    > > Xerox-clone[1] (snicker)?
    > >
    > > Thanx,
    > > Tarkin
    > > [1] I am old enough to remeber when mimeographs
    > > were replaced, the new process was called
    > > "Xeroxing".

    >
    > I remember "using" mimeograph machines. Xerox didn't exist at that
    > time. :-)
    >
    > My reason for suggesting the 820-1, or bigboard for that matter, is
    > that it is a fairly stable starting point. I have know idea of the
    > skills of the readers of this list so thought a known starting point
    > would be good. I had an 820-1 many years ago. It reminded me of two
    > aircraft carriers parked side by side. :-) That puppy was big!
    >
    > Anyway, the design could be simplified and then expanded on. My 820 was
    > hacked to the max. I had doubled the speed from 2.5 to 5 MHz, added the
    > double density adaptor, hard drive interface, 68000 co-processor and
    > changed the video timing to use a hercules monitor. It looked more like
    > a high rise apartment complex than a computer board. :-)
    >
    > Don


    How about a modular approach?

    Sort of like a PC102 concept. We design seperate boards with some sort
    of 'universal' bus, and people choose what features they want, beyond
    the basic cpu board.

    One board for video, another for IDE..

    Of course everything will need to be done with CPM in mind, but i would
    think a modular approach would make it fit most anyones needs.

    ( spending this weekend myself digging for z80 books in my garage, and
    see what chips i have left .. its been a while but i think this might be
    just the excuse to dust off all my old equipment, and braincells, and
    actually do something with real hardware again. Going thru life as a
    software guy is hard for an old EE like me )

    Or am i way off base here in this day and age and should just be content
    with my z80 card in my IIGS?

  11. Re: Home built Z80 computers

    Darn your socks!! Is it fun (the IIgs + card)?

    I am having fun with the C128. I RTFM for
    once, and realized you CAN use cp/m
    in the 40-col tv mode. So I knocked around
    with Mac and Ed. Fun stuff!!
    (*Thank You ETG!!!!*)

    I have a couple of proposals for a middle
    ground on this.

    If the CPLD's are that low, I am guessing
    that their gate count is as well.. So design
    the glue logic in such a manner as to allow
    implementation as a single CPLD or a handful
    of 74-series logic devices. Combined with
    the idea of either reserved ports or addy's,
    this would leave a design that is consistent
    (from a software point of view), but gives
    a lot of room for the indiviual implementor.
    Leftover gates could be connected to the
    reserved ports/addy's to provide custom
    peripherals- like ISP or video or audio
    or cassette controls. The core chips-
    uP, disk controller, ram, rom, sio,
    ctc, pio, etc all need their specific pins
    tended to. It will simply be left to the
    individual to choose which 'black box'
    he sticks between those chips.

    Don - got any links to specific vendor's
    pages on CPLD's in that range, and/or
    the tools? I'm going to google up on
    JTAG & connectors for same. I guess
    I should come out of the 80's.

    "Take, on, meeeeee......."
    (take on me)
    "Taaaake meee onnn...."
    (take on me)
    "I'lll beeee gooooneeeeee......'

    -Tarkin


  12. Re: Home built Z80 computers

    Feel free to get a space on my website. I can create a personal page
    for you or just for the project itself, as you like.
    Simply let me know if you're interested in this space.
    This also is giving me the idea that ALL of the works of this thread
    can be hosted on my server if the people here likes the idea.
    It would be nice to create a dedicated forum on the site too....


  13. Re: Home built Z80 computers

    Oops! i forgot to say that my last post about web space, was in
    response to Lee Hart:
    > I don't have a website, but would be happy to post the schematic or
    > board layout. Anyone have any suggestions on where to put them?


    Sorry.
    -Piergiorgio


  14. Re: Home built Z80 computers

    In article <1145328224.554297.3460@j33g2000cwa.googlegroups.co m>,
    "Tarkin" wrote:

    > Darn your socks!! Is it fun (the IIgs + card)?
    >
    > I am having fun with the C128. I RTFM for
    > once, and realized you CAN use cp/m
    > in the 40-col tv mode. So I knocked around
    > with Mac and Ed. Fun stuff!!
    > (*Thank You ETG!!!!*)
    >
    > I have a couple of proposals for a middle
    > ground on this.
    >
    > If the CPLD's are that low, I am guessing
    > that their gate count is as well.. So design
    > the glue logic in such a manner as to allow
    > implementation as a single CPLD or a handful
    > of 74-series logic devices. Combined with
    > the idea of either reserved ports or addy's,
    > this would leave a design that is consistent
    > (from a software point of view), but gives
    > a lot of room for the indiviual implementor.
    > Leftover gates could be connected to the
    > reserved ports/addy's to provide custom
    > peripherals- like ISP or video or audio
    > or cassette controls. The core chips-
    > uP, disk controller, ram, rom, sio,
    > ctc, pio, etc all need their specific pins
    > tended to. It will simply be left to the
    > individual to choose which 'black box'
    > he sticks between those chips.
    >
    > Don - got any links to specific vendor's
    > pages on CPLD's in that range, and/or
    > the tools? I'm going to google up on
    > JTAG & connectors for same. I guess
    > I should come out of the 80's.
    >
    > "Take, on, meeeeee......."
    > (take on me)
    > "Taaaake meee onnn...."
    > (take on me)
    > "I'lll beeee gooooneeeeee......'
    >
    > -Tarkin


    I have a C128 as well And an osborne 1 ( though the keyboard is
    acting up and isnt reconized at all... )

    Xilinx has inexpensive CPLDs and FPGAs. Plus their design tools are free
    for home use.

  15. Re: Home built Z80 computers


    Tarkin wrote:
    > Darn your socks!! Is it fun (the IIgs + card)?
    >
    >
    >
    > If the CPLD's are that low, I am guessing
    > that their gate count is as well.. So design
    > the glue logic in such a manner as to allow
    > implementation as a single CPLD or a handful
    > of 74-series logic devices. Combined with
    > the idea of either reserved ports or addy's,
    > this would leave a design that is consistent
    > (from a software point of view), but gives
    > a lot of room for the indiviual implementor.
    > Leftover gates could be connected to the
    > reserved ports/addy's to provide custom
    > peripherals- like ISP or video or audio
    > or cassette controls. The core chips-
    > uP, disk controller, ram, rom, sio,
    > ctc, pio, etc all need their specific pins
    > tended to. It will simply be left to the
    > individual to choose which 'black box'
    > he sticks between those chips.
    >
    > Don - got any links to specific vendor's
    > pages on CPLD's in that range, and/or
    > the tools? I'm going to google up on
    > JTAG & connectors for same. I guess
    > I should come out of the 80's.
    >
    > "Take, on, meeeeee......."
    > (take on me)
    > "Taaaake meee onnn...."
    > (take on me)
    > "I'lll beeee gooooneeeeee......'
    >
    > -Tarkin


    A modular approach would be an excellent idea. Take the video circuit
    like that on the bigboard or xerox as an example. All those counters
    and glue logic to generate the sync and video signals could be drawn as
    a single sub-circuit using your favorite TTL logic. That same circuit
    could also be run through a logic compiler to produce the data file
    needed to program a single CPLD. Now you have two ways to go to get to
    the same result.

    The GIDE is another perfect example. The 74xx646 is getting hard to
    find and the design uses two of them plus a 16V8 and 20V8 GAL. The
    whole thing would fit in a single CPLD.

    All of the memory and I/O decoder logic is another place that a CPLD
    could be used to good advantage.

    I will start another discussion and share what I know about CPLD's.

    Don

    P.S. Please excuse my spelling and bad grammer. Not to bother anybody
    with my problems but I have dyslexia which makes my spelling bad and my
    ability to express myself in words next to impossible.


  16. Re: Home built Z80 computers

    Yes Don! That's what I meant exactly.

    ziggy: I have two Kaypros that I am hoping
    to Frankenstein into one working beasty.
    The keyboard issue on your Osb is probly
    due to either corrosion or connector
    mechanical failure, IIRC some of the
    previous discussions from this very board.
    A dis-assembly and inspection of the kb and
    connectors may well be in order.
    (>>for an old EE like me oops!
    why am I giving you advice on hardware?
    )


    CPLD's in the 6-12 $ range....how sharp is the
    learning curve on VHDL? (or what's that other
    whiz-bang language?). You guys are tempting
    me w/ the dark side....

    While trying to read up on the BB, one site
    quoted someone as saying the Kaypro was so
    similar (to the BB) that it was considered by
    some to be an unlicensed copy. If that's the
    case, or if the video systems are even vaguely
    similar, then I am for tty. The Kaypro's video
    section makes my heard spin when I try to
    comprehend it. Video is one place I'd
    definitely go in for using a CPLD or
    even a microcontroller (a la VCR Pong),
    so as to keep it's headaches separate from
    the rest of the system. Divide and conquer,
    I say.

    In any event, I feel that either a tty, a manual-
    entry (switches/keypad)+lcd, or both should
    be in place as a development bootstrap and
    emergency system saver. As a not-quite-
    expert linux user who likes to run as root,
    I usually keep a small partition on my linux
    machines w/ a 'stock' distro like slackware 8
    or mandrake 7.2 or RH 6 in case I screw up a
    script and lock myself out of my (main) system.
    I also keep bootable cd toolkits (linuxcare BBT)
    and flopppies (tomsrtbt). I may not use those
    failsafes regularly, but they darn sure are handy
    when the unexpected happens.

    TTFN,
    Tarkin

    p.s before I get flamed by 'professional'
    linux users, the machines that I run as root
    on are *not* production servers or mission-
    critical; I have no sensitive data on them.
    Running as a separate user and having to su
    everytime I wanna clip my toenails just
    irritates me.


  17. Re: Home built Z80 computers

    Don wrote:

    > A modular approach would be an excellent idea. Take the video circuit
    > like that on the bigboard or xerox as an example. All those counters
    > and glue logic to generate the sync and video signals could be drawn as
    > a single sub-circuit using your favorite TTL logic. That same circuit
    > could also be run through a logic compiler to produce the data file
    > needed to program a single CPLD. Now you have two ways to go to get to
    > the same result.


    > The GIDE is another perfect example. The 74xx646 is getting hard to
    > find and the design uses two of them plus a 16V8 and 20V8 GAL. The
    > whole thing would fit in a single CPLD.


    What's the deal with the 74x646? Fairchild is currently making them.
    You can get them from Mouser, but not Jameco.


    --
    David Griffith
    dgriffi@cs.csbuak.edu <-- Switch the 'b' and 'u'

  18. Re: Home built Z80 computers


    "Dave Griffith" wrote in message
    news:3Yj1g.12385$4L1.12152@newssvr11.news.prodigy. com...
    > What's the deal with the 74x646? Fairchild is currently making
    > them.
    > You can get them from Mouser, but not Jameco.


    Jameco carries the 74ABT646 version - I've purchased 40-50 of them.
    I've used 646 chips from the F, ALS, HC, and ABT families - all work
    as intended in the GIDE.


    Terry



  19. Re: Home built Z80 computers

    "Don" writes:

    >A modular approach would be an excellent idea. Take the video circuit



    >The GIDE is another perfect example. The 74xx646 is getting hard to
    >find and the design uses two of them plus a 16V8 and 20V8 GAL.



    >All of the memory and I/O decoder logic is another place that a CPLD
    >could be used to good advantage.


    How about the Floppy-Controller?
    It might be difficult to get a real 40-pin Chip these days; even
    a version for the IBM-PC with some other IO may be hard to get...

    Would it be possible to do a 765 like AND a WD-like controller
    into one CPLD with the possibility to dynamically re-program that
    chip 'on the fly'? I preferred th WD chip in those old days. And
    I once had to read a Floppy with 128 Bytes in DD, which would
    have been impossible on the 765.

    Just asking, Holger

  20. Re: Home built Z80 computers


    Terry Gulczynski wrote:
    > "Dave Griffith" wrote in message
    > news:3Yj1g.12385$4L1.12152@newssvr11.news.prodigy. com...
    > > What's the deal with the 74x646? Fairchild is currently making
    > > them.
    > > You can get them from Mouser, but not Jameco.

    >
    > Jameco carries the 74ABT646 version - I've purchased 40-50 of them.
    > I've used 646 chips from the F, ALS, HC, and ABT families - all work
    > as intended in the GIDE.
    >
    >
    > Terry


    Terry and Dave. I stand corrected on the 74xx646. I typically look for
    the LS, HC & HCT parts which I didn't find until I looked at the
    B.G.Micro catalog. I did find the parts previously mentioned in the
    DIGI-KEY and Jameco catalogs. While Mouser is a good source of parts I
    have never used them so didn't look there.

    The one thing I like about these groups is that while one person my not
    have all the answers or may have incomplete information, collectively I
    think we have all the bases covered.

    Don


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