[HN Gopher] Build an 8-bit home computer with 5 chips
___________________________________________________________________
Build an 8-bit home computer with 5 chips
Author : lelf
Score : 240 points
Date : 2020-03-21 09:13 UTC (13 hours ago)
(HTM) web link (spectrum.ieee.org)
(TXT) w3m dump (spectrum.ieee.org)
| sigmaprimus wrote:
| If modern harware is going to be used, wouldn't a FPGA be a good
| way to replace the TTL devices thus lowering chip count?
| grugagag wrote:
| I wonder, How much can these 8bits computers be pushed in terms
| of overclocking the cpu / replaced with a new cpu?
| Gracana wrote:
| You can get a 20MHz Z80 that will overclock up to 33MHz or so.
| A Z8S180 runs at 33MHz and includes timers, uarts, dma, and an
| MMU. I don't know how much you could overclock one of them, but
| it's already pretty fast for an 8-bit chip.
|
| Zilog also makes the ez80, which is like the Z180 but runs at
| 50MHz and has a 3 stage pipeline, and it has a 24-bit mode.
|
| On the 6502 side, there's the 65C816S which is the fully-static
| CMOS version of the 65816, which is a 6502-compatible CPU with
| a 16 bit mode and 24-bit addressing. The Apple IIgs had one,
| but its clock speed was limited to 2.8MHz so as not to compete
| with the Macintosh. Today you could build a machine with a
| 14MHz 65C816S and fast SRAM, and have a pretty beastly
| 6502-compatible machine.
| LeonM wrote:
| Depends on your definition.
|
| If you don't care about socket compatibility you could simply
| load an 8-bit CPU in a fast FPGA. It will probably not be hard
| to run one at 100MHz or so.
| tyingq wrote:
| Just to confirm...128MHz Z80 via an FPGA.
| https://sowerbutts.com/socz80/
| grugagag wrote:
| Thanks. I meant in terms in desicated parts but FPGA might do
| it. I think we need some starter computers for kids and 8 bit
| seems quite a good choice. A lot of us started with them and
| they were simple enough so we could program them ourselves.
| Gracana wrote:
| There's a big community built around DIY Z80 systems, if
| you're interested in that sort of thing.
|
| Grant Searle's breadboard CP/M machine:
| http://searle.x10host.com/cpm/index.html
|
| Spencer Owen's RC2014 modular bus-based Z80 system:
| https://rc2014.co.uk/ Highly active RC2014 discussion
| group: https://groups.google.com/forum/#!forum/rc2014-z80
|
| Phillip Stevens' beautiful YAZ180 Z180-based SBC:
| https://github.com/feilipu/yaz180
|
| z88dk, a Z80 C cross compiler with libraries and all sorts
| of useful things, which supports many machines:
| https://www.z88dk.org/forum/
|
| Jon Langseth's LiNC80: http://linc.no/products/linc80-sbc1/
|
| Steve Cousins' many different machines, some
| RC2014-compatible, some z50bus (LiNC80) compatible, some
| Z180 stuff, SBCs, a powerful "small computer monitor", etc:
| https://smallcomputercentral.wordpress.com/projects/
|
| Alan Cox's Fuzix, a unix for 8-bit machines (including many
| of the aforementioned Z80 machines):
| https://github.com/EtchedPixels/FUZIX
|
| Most of the folks mentioned can be found on the retro-comp
| discussion group, which was formed from RC2014 group
| members to discuss other projects:
| https://groups.google.com/forum/#!forum/retro-comp
| jejones3141 wrote:
| People have run Hitachi 68C09Es at 5 MHz. May not sound like
| much, but the 6809 (which the 6309 is an improved version of)
| takes fewer clock cycles than Z-80 or 808x take to do similar
| work. OpenCores has a 6809 core, not cycle accurate, that can
| run at 40 MHz if I understand the description rightly
| (https://opencores.org/projects/6809_6309_compatible_core).
| black_puppydog wrote:
| Very cool project! I'm not sure exactly _why_ , but the idea of
| having a self contained computer that you plug into any display
| still seems appealing to me, even though I'm typing this on a
| convertible laptop that actually brings its own display...
| SeaSeaRider wrote:
| Website completely broken for EU mobile traffic. GDPR popup
| hidden under another popup (yay 2020) and page cannot be scrolled
| or viewed.
| ratww wrote:
| _> GDPR popup_
|
| I will die on that hill but that "GDPR popup" is actually a
| pre-GDPR, obsolete cookie law popup that is not compliant with
| GDPR anymore (GDPR requires ability to deny cookies) and should
| be removed, as it amounts to nothing and is a pretty much a
| dark pattern. (I upvoted you btw, because I agree 100%)
| a1369209993 wrote:
| Also completely broken from (I think) US residential IP
| addresses (wget'ed html does not contain page text at all).
| robin_reala wrote:
| I'm not seeing that (Firefox anti-tracking?) but it's trivial
| to hit the reader mode button in the address bar: it's a better
| experience anyway.
| cl3misch wrote:
| If you wait long enough, the obstructing popup goes away ;-)
|
| One of the rare occasions where I endured such pain because I
| was so interested.
| aiCeivi9 wrote:
| Looks ok for me, with adblock+umatrix:
| https://i.imgur.com/UABzai9.png
| abdullahkhalids wrote:
| The way the website is setting the title is weird. On my Debian
| XFCE4 toolbar, the title is showing in two lines.
|
| https://imgur.com/ADhL9Aj.png
| lucidguppy wrote:
| I wish the spectrum next would get a wider release. I know that
| the raspberry pi was supposed to be the hobby computer of our
| age, but I just really like the simplicity combined with all of
| the paint point removal of the 8bit age.
| jsjohnst wrote:
| > It uses just six integrated circuits--a CPU, USB interface, and
| four 7400 chips
|
| Wonder how the source article came up with the title "just 5
| chips", yet the article throughout mentions six. Not a huge deal,
| but wonder if typo or some other reason?
| ujuj wrote:
| If i understood correctly, the USB interface is optional, as
| printed on the pcb.
| mrlambchop wrote:
| Love the write up. OSHPark PCBs - wondering how many revisions it
| took to get that keyboard layout working! I'd love an 8bit era
| keyboard and case that you can plug your own PCB into - I'm
| itching to design something from scratch but I know what will
| happen if I need to do a full cycle design process - eventual
| apathy :(
| russellbeattie wrote:
| I recently bought Ben Eater's 6502 kit. One of the things I've
| been meaning to do is figure out how to get it to talk to a
| serial port for terminal access.
|
| A while ago on YouTube, I watched a series where someone was
| restoring their IMSAI 8080 (the machine from WarGames) and
| learned it and the original Altair were a lot more capable than
| their front panels made them seem due to the S-100 expansion
| slots inside that sit on the bus. The first card the video showed
| was a terminal connection so he could send/receive commands using
| a VT-100 terminal (an emulator on a normal PC in this case). The
| cool thing I learned is that the way this worked is that the
| terminal board on the IMSAI would simply send the same screen
| info over and over again across the serial port, and it was up to
| the terminal to display this data on screen (making terminals
| like little dedicated computers themselves). I don't know how I
| thought this worked, but it was cool to see him debugging it.
|
| Seems a lot easier than trying to get a direct-connected display
| up and running and having to figure out all the signals and
| colors, etc. That said, I haven't actually done this yet, so the
| devil may be in the details.
|
| 1. https://eater.net
|
| 2. https://youtu.be/d_mWREmze5o
| msarnoff wrote:
| Hi HN, project author here. The source code and design files are
| on GitHub: https://github.com/74hc595/Amethyst
|
| Documentation is lacking, sadly. My intent was to create a series
| of in-depth videos describing how various aspects of the system
| work in detail, but I'm somewhat behind on that.
|
| For folks that say "using an ATMEGA is cheating":... I agree!
| That was a guiding principle behind my 6809 computer project
| (Ultim809)--use only period hardware and no programmable chips
| (apart from EPROM). Amethyst originated a bit differently.
| Initially it started out as a neat hack to get 8-bit color video
| from a non-overclocked AVR without expensive external chips. And
| then I discovered the mechanical keyboard community and was able
| to source keyswitches and keycaps, and, well, in for a penny, in
| for a pound.
| JKCalhoun wrote:
| Matt, you're rockin'. Saw a link to this on YT via
| /r/mechanicalkeyboards
|
| I like the staggered key arrangement of your prototype better,
| but whatever.
|
| Your projects always inspire me.
| moralsupply wrote:
| Why not take some of the discrete components out and introduce
| another cpu to handle both video and sound? it would make the
| design much simpler and programming easier overall.
|
| Also, why not use a more capable cpu with more embedded ram?
| These things are very cheap nowadays.
| JKCalhoun wrote:
| BTW, what is the Amethyst's story regarding modern displays?
| Most of us have tossed our CRTs.
| MuffinFlavored wrote:
| For this project, how are the 4KB of EEPROM used differently
| than the 16KB of application memory?
| teddyh wrote:
| > _Consequently, I needed a lightweight programming environment
| for users, which led me to choose Forth over the traditional
| Basic._
|
| Excellent! I've always maintained that BASIC is a bad language
| for memory- and CPU-constrained systems.
| funkaster wrote:
| can't talk about 8bit minimalistics homebrew computers without
| mentioning Uzebox:
|
| http://uzebox.org/wiki/Main_Page
|
| it's a great platform, super easy to develop, tons of fun. Highly
| recommended.
| thought_alarm wrote:
| Direct link to GitHub project:
| https://github.com/74hc595/Amethyst
| [deleted]
| rkagerer wrote:
| _Can you shave a chip or two off the count?_
|
| MCU with integrated USB? eg. A SAML21 chip. It also has several
| PWM timers, CCL and DMA, I wonder if that could help with video
| generation?
| Jaruzel wrote:
| The problem here is, it's hard to get decent video output without
| a larger set of complex chips. If you just want serial output,
| this is totally doable with period accurate chips.
|
| There are quite a few Z80 implementations that only use a handful
| of chips.
| mysterydip wrote:
| RC2014 mini comes to mind:
| https://rc2014.co.uk/modules/rc2014-mini/
| dmitripopov wrote:
| A friend of mine, an 8-bit enthusiast, calls usage of ATMEGA
| chips "cheating" :) "True" 8bitter relies solely on component
| base of the 80s.
| tyingq wrote:
| Meh. The spirit of a self contained unit (display output,
| keyboard input, etc) and boot-to-interpreter are there. The
| Maximite family of boards "cheat" even more with a PIC32. But
| they are popular, and have the same feel as the 80's 8 bit PCs.
| dmitripopov wrote:
| Yes, but it's not about the feel of the product which is
| definitely there, but about the skills required to design. I,
| personally, would never call anybody who designed his own
| computer whether with ATMEGA or not, a "cheater". It deserves
| respect, to say the least.
| [deleted]
| hyperpallium wrote:
| ZX81, from 1981, used 4 chips.
| dmitripopov wrote:
| Well, his argument is not about the number of chips but
| rather component origins. If you are about to pretend that
| you are in the 80s and you develop a computer in that time,
| you've got to use what was available. I argue that ZX
| Spectrum used custom-made ULA and you kind of emulate that
| approach to design with ATMEGA and he just laughs :)
|
| The truth is that we live in magnificent times where there's
| a wide range of choice on how to do things and it is amazing.
| jeadfa wrote:
| The Travelers Talk - Getting Your Travel Information
| https://thetravelerstalk.com/
| [deleted]
| fred256 wrote:
| One of which was custom designed (an ULA) for the ZX81.
|
| The ZX80 used 21 (IIRC) off-the-shelf TTL chips.
| lvturner wrote:
| Saw this a few times on HN, but immediately thought of it and
| feel its an appropriate response to your friend.
|
| "I thought using loops was cheating, so I programmed my own
| using samples. I then thought using samples was cheating, so I
| recorded real drums. I then thought that programming it was
| cheating, so I learned to play drums for real. I then thought
| using bought drums was cheating, so I learned to make my own. I
| then thought using premade skins was cheating, so I killed a
| goat and skinned it. I then thought that that was cheating too,
| so I grew my own goat from a baby goat. I also think that is
| cheating, but I'm not sure where to go from here. I haven't
| made any music lately, what with the goat farming and all."
| coupdejarnac wrote:
| If your goal is to reduce the problem domain from hardware
| and software to just software, then yeah, using a chip with
| most of the hardware work done for you is fine.
|
| Looking at Ben Eater's youtube channel, there seems to be a
| healthy demand for building more authentic '80s 8-bit
| systems.
|
| If one's goal is to learn about how to build an 8-bit
| computer, using a microcontroller is not going to be an
| edifying experience unless the goal is to do something mostly
| in the software domain like write a simple OS.
|
| While I think your parable is good advice for getting a
| business going quickly, it's not appropriate for deep dive
| learning or hacking.
| lalalandland wrote:
| Yes, it's silly to be gate keeping like this, with some
| purist fantasy. If OP friend like to role play as a engineer
| from 1981, that is cool. But he has to realize that that is
| not everybody's goal.
| okareaman wrote:
| Beautiful. The law of diminishing returns means that the
| perfect is the enemy of the good (or something like that.)
| sjwright wrote:
| The lesson is that when it comes to personal pursuits,
| there are no bright lines between doing something
| "properly" or "cheating". It truly is all in the eye of the
| beholder.
| dmitripopov wrote:
| I see what you are talking about, but your parable has
| another side that no one sees - the guy learned a lot of
| different things in the process :) For people who enjoy
| learning and exploration it is the true meaning of the whole
| thing, not a written tune.
| dahart wrote:
| > your parable has another side that no one sees - the guy
| learned a lot of different things in the process
|
| No one sees?! What do you mean? That's literally the punch
| line of the joke.
|
| Of course 'learning things' is a secondary benefit,
| especially if that's actually one of the goals you
| specifically set out for. Still I've personally watched
| programmers live that joke, and overengineer something that
| could take a day into a year long project, to solve a
| problem they didn't have. I've seen it enough and cause
| enough problems that I try hard to write code with
| specificity and stick to the problem at hand. So much so
| that I have an actual problem with not abstracting things
| soon enough. ;)
| dmitripopov wrote:
| Well, I just thought you are giving a negative
| connotation to it while I think there's nothing wrong if
| the thing is your hobby :)
| joefourier wrote:
| While clever, I'm not a fan of this argument as it ignores
| the fact that each of steps are different things requiring
| different skills. Putting samples together is more arranging
| music, while creating the notes is composing. After that, you
| have sound design, playing an instrument, making an
| instrument yourself...
|
| Sure none of these are "cheating", but someone somewhere has
| to do each of those things, and the further down the chain
| you go, the more "control" you get over your sound and
| composition. The law of diminishing returns of course hits at
| some point (although someone may argue that their breed of
| goats has a certain sound they can't get any other way).
|
| It's the same thing in programming: someone chaining together
| libraries may eventually run into a point where there's
| nothing out there that does exactly what they need. That
| doesn't mean it's not your work unless you've written the
| compiler yourself, or have your own fab in your garage, it
| just means you have to be aware of the degree of control you
| give up the higher level you go.
| tomxor wrote:
| It doesn't sound like you are in disagreement, the parent
| story is just a flowery expression of the diminishing
| returns (control), the further you go.
|
| As you say, the reality of it is that there are thresholds,
| for some where the benefit cost ratio is poor enough few
| will break through it from a higher level use... and then
| there are lower ratio thresholds in between where you will
| get various proportions of experienced people who want a
| little more control (in different directions) breaking
| through.
|
| But even with those thresholds (in this case one IC vs
| another IC), it's arbitrary and subjective, you are just
| choosing to spend your time and effort in a different way.
| JNRowe wrote:
| Love that description.
|
| In many ways watching people describe and choose their spot
| in the "grab package" <-> "herd goats" spectrum is my
| favourite part of AoC each year1. The squirming some people
| choose to do when justifying their place in a table of magic
| internet points is a lot of fun.
|
| _Edit_ : Should add I'm one of those squirmers too, often
| when I'm thinking about networkx/numpy/etc.
|
| 1. https://adventofcode.com/
| perl4ever wrote:
| I have found satisfaction at least for now in going in the
| other direction - what can I do with a locked down computer
| that has absolutely no software installation authorized and
| only has the standard software for any non-technical
| employee. In other words, _everything_ that can 't be done
| in that environment is now "herding goats" to me. Sometimes
| I am tempted to try to get developer-type privileges, but
| I've resisted so far.
| JNRowe wrote:
| Is there an endgame beyond empathy for "normal" users?
| I'm curious about whether you're doing this to learn more
| or perhaps with the intent on spotting opportunities to
| make things better or some other reason entirely.
|
| I can personally see the discussion of how to work with a
| basic installation being worthwhile, as I know I'm guilty
| of "why don't you just $bunch_of_experience_option?".
| However, I don't think I'd want to try to do actual work
| without the tools I have and the tools I make.
| perl4ever wrote:
| For an auto metaphor, suppose you were really good at
| building race cars, and then you set out to make an entry
| for the 24 hours of LeMons.[1] Some people do that. I
| never have been a blank sheet of paper/greenfield sort of
| person and I always lose interest in computer games if I
| have unlimited resources.
|
| [1] https://en.wikipedia.org/wiki/24_Hours_of_LeMons
| derefr wrote:
| That's not much of a constraint--the
| https://en.m.wikipedia.org/wiki/Hudson_Soft_HuC6280 was an
| 8-bit CPU produced in 1987, and yet was powerful enough (in
| combination with the PC Engine's 16-bit PPU) to drive very rich
| experiences.
| phire wrote:
| Personally I don't care that it's a modern "90s" chip.
|
| But the fact that it's a microcontroller rather than a
| microprocssor bugs me. The lack of an external memory bus feels
| incredibly in-authentic to me.
| tyingq wrote:
| Many of the ATMEL 8 bit chips do have an external memory bus.
| Not used in this case, but it's possible.
|
| Sometimes it's pretty blurry what is a microcontroller and
| what is a microprocessor. The PIC32MZ/DA has an integrated
| Graphics Controller and 32MB of DRAM.
| Gracana wrote:
| The AVR can't execute programs from the data bus, which
| means no execution from RAM or external memory, though you
| could write a virtual machine that could do so.
| pinewurst wrote:
| http://geoffg.net/maximite.html
|
| That's a cool PIC32 home computer - PIC32 is MIPS btw far
| beyond the old 8 bits though...
| girvo wrote:
| There's a BSD 2.11 port for PIC32:
|
| http://retrobsd.org/wiki/doku.php/start
| phkahler wrote:
| >> The lack of an external memory bus feels incredibly in-
| authentic to me.
|
| Yep. It's still a neat project, but don't claim to build an
| 80's computer using "only 5 chips" when they're more modern
| chips that allow that low count. A single FPGA can do it all
| too.
|
| On a tangent, I'm curious about upgrades to old machines that
| could have been done at the time. For example, my Interact
| has super low-res graphics where each pixel is 3 scan lines
| high. That machine was designed for 4-8K of ram but shipped
| with 16K and had an upgrade to 32K. It seems like increasing
| the vertical resolution should have been a fairly trivial
| hardware hack since the RAM is all there. Bumping the
| horizontal resolution might have been possible but harder.
| Increasing the available colors should have been fairly easy.
| It seems to be a case of not enough time for the design to
| bake. The other 8bit machines with ASICs might not be so
| incomplete, but there may still be some things that could
| have been done.
| tenebrisalietum wrote:
| A lot of 8 bit designs used designed ASICs that weren't a
| generally available part, like the Atari 2600 with the TIA, the
| Commodore 64 with the PLA, etc. Using microcontrollers for
| these seems fair.
| rbanffy wrote:
| You could do a lot with period-correct SoCs like the 8052.
|
| https://archive.org/details/BYTE_Vol_10-08_1985-08_The_Amiga...
| pritovido wrote:
| Steve Wozniak himself was cheating. Instead of using proper D/A
| converters that costed 100 times more, he made a hack.
|
| And the hack was good enough.
|
| It is one of the things in which academical training is
| perverse. It trains you to always complicate more and more any
| subject, and that the hard work is the goal, shortcuts are not
| permitted.
| glouwbug wrote:
| What was the hack? PWM to an RC filter?
| Cyberdog wrote:
| I believe it's the one mentioned in the article about how
| to achieve a color NTSC signal by just outputting ones and
| zeroes with proper timing.
|
| It begs the question what was done in parts of the world
| that didn't use NTSC, though.
| fsckboy wrote:
| the other video standards (Europe used PAL) aren't much
| different in principle than NTSC, just some different
| timing and encoding parameters, the same D to A
| techniques work. PAL is higher bandwidth (and higher
| quality) than NTSC and Woz's timings were on the edge for
| NTSC so PAL versions didn't do color till a little later.
| dmitripopov wrote:
| I agree. But, you know, enthusiasts enjoy holywars. And
| there's a thin hazy line between a "true" and a "cheater".
| rzzzt wrote:
| The display controller chip seems to be a hard to source part
| if you want to stick to 80s components. Do you know what his
| recommendation would be for that piece?
| transitorykris wrote:
| Yes, that's been a frustration for me. I've settled on the
| Motorola 6847 which requires a couple supporting chips. This
| is scavenging parts off eBay though, which seems to be a
| plentiful source. I'll find out shortly whether any of them
| are actually good.
| snarfy wrote:
| It looks like it would take about 20 chips. [1]
|
| [1] - https://eater.net/vga
| rzzzt wrote:
| Not an unreasonable choice, but it has to be noted that
| home computers of the era already used LSI/VLSI dedicated
| ICs for this purpose, condensing the functionality of these
| 20 chips into a single package.
| FabHK wrote:
| Does anyone know how many chips the Sinclair ZX-81 had?
| UncleSlacky wrote:
| Four - CPU, RAM, ROM & ULA.
| zokier wrote:
| 5, but ZX81 had (semi-)custom logic chip so its not that
| directly comparable
| epx wrote:
| Every keyboard (or at least an AVR-based DIY open-source
| mechanical keyboard) is an 8-bit computer. Toyed many times with
| the idea of adding a display to a keyboard I assembled.
| glouwbug wrote:
| And for those wondering how much power resides in an 8 bit 20 MHZ
| AVR with 3 or 4 colors and sound over RCA checkout Craft by IFT:
|
| https://youtu.be/sNCqrylNY-0
|
| It is as good as domain specific mastery gets
| fortran77 wrote:
| Try to reproduce that with a modern stack, and you'd need
| hundreds of megabytes of browser engines, npm libraries, etc.
| and a GHz clock speed.
| Craighead wrote:
| or in reality just dosbox?
| dokem wrote:
| Embedded software development is still alive and well. No js
| required.
| fortran77 wrote:
| Sure. I said with a modern stack, like what most webs __*s
| program in.
| ardy42 wrote:
| That's a _really odd_ keyboard layout: querty that omits the
| spacebar and puts space under _backspace_.
| carapace wrote:
| I have a bunch of atmega328p microcontrollers hanging around from
| a previous project. I'm _so_ tempted to try to make some kind of
| bit-sliced CPU out of them...
___________________________________________________________________
(page generated 2020-03-21 23:00 UTC)