ZX Spectrum build, No ULA.

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Күн бұрын

In this short series, I'm going to build a ZX spectrum using an EPROM instead of a ULA. In this video, much of the build is done and some bring-up.
I'm planning to do a PAL version as well.
16K ZX81 vs 16K ZX Spectrum
• 16K ZX81 vs 16K ZX Spe...
VGA from an EPROM.
• VGA from an EPROM, is ...
Apple 2 wire-by-wire
• Apple 2 wire-by-wire b...

Пікірлер: 103

@alexloktionoff6833 4 ай бұрын

This is what I was looking for - all discrete no rare ULA and DRAM and VGA output! Please continue

@DrMattRegan 4 ай бұрын

Enjoy!

@andrewkieran8942 4 ай бұрын

I came to watch this to understand your approach, and how you'd solve the timing issues. Then, I was impressed with your construction technique. Those things are all impressive, but then I fell in love with the pic of your puppy!!

@DrMattRegan 4 ай бұрын

Yeah she's great. Normally I'm very allergic to dogs (and cats), but she's a cavoodle and no allergic reaction at all!

@mheermance 4 ай бұрын

Neat. Your point to point wiring looks so much better than mine. I find that when I am halfway through I realize I have painted myself into a corner, and the latter half of the build is trying to avoid melting wires from the first half.

@DrMattRegan 4 ай бұрын

Exactly! I do have that problem later as well, it happened a bit on the SAP6502 build. Some pins were several wires deep.

@csbluechip 4 ай бұрын

Can you make a short video showing how you are doing the wiring please. Especially one (bus) wire to multiple points. It's not obvious where the insulation is coming from. Loving this series. Thanks

@DrMattRegan 4 ай бұрын

Thanks, will be working on a build techniques video soon.

@AndyGraceMedia 4 ай бұрын

This is absolutely gold. Loving it. Really clever solution to the problem. On construction technique I'm also impressed. I think I'd lose the plot with that sort of point-to-point IC socket wiring. I've prototyped using soldered break-off SIP machine-pin sockets designed for wirewrap and that was hard enough.

@DrMattRegan 4 ай бұрын

Thanks Andy, it's a fun little project. It should end up at < 30 chips.

@AjinkyaMahajan 4 ай бұрын

Impressive work !!!

@DrMattRegan 4 ай бұрын

Thank you! Cheers!

@kirknelson156 4 ай бұрын

thats some genius level problem solving, enjoying the series 🙂

@DrMattRegan 4 ай бұрын

Thanks for that, glad you like it.

@flomojo2u 4 ай бұрын

Wow, what a blast from the past! I built SO many little embedded boards using those Radio Shack prototyping boards and blue Kynar wire. I stuck with 68000-series CPUs, including a 8MHz 68000, 16MHz 68020, and 33MHz 68030. They all worked great, though I used PEEL programmable logic for decoding the addressing signals for the 68020/030 boards. Very simple boards, mostly EPROM/flash, SRAM, logic, and random stuff, including an IDE hard drive using my own file system. It was lots of fun reading the ATAPI specification for all the registers and commands!

@DrMattRegan 4 ай бұрын

Excellent. I'm thinking of doing a series like the kzfaq.info/sun/PLjQDRjQfW-85S5QkX8wZbkqichM6TLYYt but for the 68000, a TTL-68000 CPU. Would that be of interest?

@schrodingerscat1863 4 ай бұрын

Personally I have always used wire wrap for projects like this but your point to point wiring technique looks great and as you point out much cheaper than wire wrap which is insanely expensive for the sockets. Using an EPROM as a replacement for the ULA is also a great idea.

@DrMattRegan 4 ай бұрын

Yeah, wire wrap sockets are hard to get in 32 pin packages.

@schrodingerscat1863 4 ай бұрын

@@DrMattRegan Can't say I have ever had problems getting any size socket but they are bloody expensive, Mouser have 23 pin DIP in stock.

@R.Daneel 4 ай бұрын

I used to do full wire-wrap, but would occasionally use this technique for parts of a circuit. One trick I used if I needed more than 2 wraps on a pin (or it was getting too busy) was to add an empty socket, wire the croweded pin to the empty socket and short socket pins together on the top of the board by sticking a wire in the socket.. You then had multiple pins to use for that one signal. Once a few pins were used this way, you could even cut off the rest of the socket with edge cutters if it wasn't needed. Sub and thumb.

@DrMattRegan 4 ай бұрын

Sounds good. I'll try that if necessary. You can sometimes get, 4 connections if you use 2 wires

@nexpro6985 4 ай бұрын

Thanks for the vid. It popped up in my yt feed. I swear KZfaq is listening to my thoughts. The last thing I did on my laptop before watching this (on my phone) was to add a map of the Zx Spectrum memory to the appendices of the Machine Lightning manual I am reproducing. The memory map indicates contended ram vs un-contended.

@DrMattRegan 4 ай бұрын

Excellent. Glad you enjoyed it. Interesting little machine the Spectrum.

@vanhetgoor 4 ай бұрын

Marvellous! This is how computers should be built. Away with the ULA, I never liked that kind of electronic parts, all that mistry, that hidden science, all those little secrets squeezed into one chip. It is a lot of work but the results are so beautiful to look at, it is craftsmanship. When the computer is not in use, you can frame it on the wall to look at.

@DrMattRegan 4 ай бұрын

Thanks for that. Back to basics. I think we should throw out the Z80 too - kzfaq.info/get/bejne/ocx9gM2cl56ck6M.html

@TheTurnipKing 4 ай бұрын

The thing is, the reason behind the ULA makes perfect sense when you see the Harlequin board, which implements the ULA in 74 series logic. Indeed, you just have to look at the complexity difference between the ZX80 and 81. It's just unfortunate that these chips had to be reverse-engineered instead of documented, they could have been reimplemented in all sorts of ways

@DrMattRegan 4 ай бұрын

Yep, the harlequin uses the same technique as the Apple 2 (and TRS 80). I used it too here kzfaq.info/get/bejne/p8iqrd2cs7atc30.html Any guesses as to why i chose an EPROM?

@schmitzbeats6102 4 ай бұрын

@@DrMattRegan I would say, to make different screen modes, via "Firmware". Like Timex 2068, Sam Coupé or ULA+

@TheTurnipKing 4 ай бұрын

@@DrMattRegan I've seen some cases where they've been used as a substitute for relatively complex logical devices, but I'd be lying if I said I understand the process here. WHY is relatively easy. PROM is cheap. How, i don't get. Yet.

@MeeBilt 4 ай бұрын

Great stuff! I used the exact same point-to-point-wire technique on my first DIY computer back in 81-82. It was based on the 6502... when I got my first job I suddenly got access to a wire-wrap gun so I used that for my next build.

@DrMattRegan 4 ай бұрын

Yep, I think they are both becoming lost arts.

@MeeBilt 4 ай бұрын

@@DrMattRegan Indeed, thanks for a great video and an interesting project! I never owned a ZX Spectrum but I borrowed one from a friend for a month to try it out - I remember those cool little micro-drives.

@DrMattRegan 4 ай бұрын

Thanks for the feedback, enjoy.

@rappzz 4 ай бұрын

Awesome! I'm sticking to Logisim for now. Seeing a physical thing run must be thrilling though 😁

@DrMattRegan 4 ай бұрын

Hope you enjoy it!

@sarkasaa 4 ай бұрын

Well, that subscription was a no-brainer!

@DrMattRegan 4 ай бұрын

Welcome. Enjoy!

@borayurt66 4 ай бұрын

Exactly. I don't understand more than half of it, but the parts that understand were enough to be hooked.

@schmitzbeats6102 4 ай бұрын

Marvelous! For quite some time I wondered how the ULA could be replaced by a giant lookup-table. You are makeing that work. Also I would appreciate a more in-depth video or article about your construction technique. Specifically which materials you use.

@DrMattRegan 4 ай бұрын

Many thanks! Yep, am thinking of putting forward a video or two on the construction technique. Stay tuned.

@billcarson9565 4 ай бұрын

Excellent, subscribed!

@DrMattRegan 4 ай бұрын

Welcome aboard!

@saszab 3 ай бұрын

Same here!

@ITGuyinaction 4 ай бұрын

👍👍👍 Excellent! Very interesting project! Even if it's not an exact "copy" of ZX Spectrum. Concerning these technical details, it's probably necessary to watch the video 2-3 times to understand everything even if the general idea is easy to catch. P.S. A bit pity that you didn't design printed circuit board.

@DrMattRegan 4 ай бұрын

I'll likely do a schematic at the end.

@ITGuyinaction 4 ай бұрын

@@DrMattRegan You mean schematic diagram or board design?

@Xsiondu 4 ай бұрын

That was awesome

@DrMattRegan 4 ай бұрын

Thanks, glad you liked it.

@garry5280 4 ай бұрын

Theres an original prototype spectrum in the cambridge computer history museum built in much the same manner.

@DrMattRegan 4 ай бұрын

Interesting. I've seen the wire-wrapped version of the first PC. I think i remember seeing one of the 68000.

@ostrov11 4 ай бұрын

спасибо, хорошая работа.

@DrMattRegan 4 ай бұрын

Glad you like it.

@DavidHembrow 4 ай бұрын

Excellent Indeed. Better than the original in terms of CPU speed. Full speed memory access in the contended memory will of course make some timing dependent software incompatible, but I'm sure you've thought of that already and I expect it to be addressed in a layer video Btw, have you tried loading the I register with 01xxxxxx ? You'll then see snow on the screen with the original hardware.

@DrMattRegan 4 ай бұрын

Thanks David. Yeah, i'll use the wait signal to slow the CPU down using the circuit in the last video to emulate the DRAM memory access. VGA will mess things up badly too, so i may do a PAL version also. I've heard about the snow issue, but i haven't looked at it in detail, I suspect the 01XXXXXX XXXXXXXX as the refresh address probably triggers the clock halt circuitry in the ULA. It triggers it during port accesses. The raster scan sweep should keep the contents of the DRAM refreshed,. Thanks for that, i'll look into it.

@alexloktionoff6833 4 ай бұрын

Actually I'd like to assemble without slow-downs, but more fast Z80 like 14Mhz @@DrMattRegan

@frankowalker4662 4 ай бұрын

Cool. And no ULA. 👍

@DrMattRegan 4 ай бұрын

Thanks, it's a fun project.

@frankowalker4662 4 ай бұрын

@@DrMattRegan I built the Harlequin 128 a couple of years ago. That was a lot of fun.

@leechatt9709 4 ай бұрын

Superb work! I did a Zx81 like that and it never worked. Interesting idea cant wait to see this clocked at 3.5Mhz. I wounder how much faster it will go especially when youve put the design on a PCB. I suppose it does work as your making videos about it? Cool! Im currently working on a Nes Emulator. the PPU runs every tick and the C6502 runs at a Modulo of 3. Are you going to release the schematic and build parts when your done.

@DrMattRegan 4 ай бұрын

It’s a work in progress. Did you use a CMOS z80? I did point-to-point wiring for a ZX81 in this series kzfaq.info/sun/PLjQDRjQfW-84WG47-5UjPz1BrXxc1acvd which did run at 3.25 MHz.

@leechatt9709 4 ай бұрын

I used a Zilog Z8400A PS. Have you ever thought of using a Teensy or a stm32 for the ULA?

@DrMattRegan 4 ай бұрын

I'd rather not use modern parts. The EPROM and SRAM were available in the 1990s. Will do a schematic once finalized.

@leechatt9709 4 ай бұрын

Cool old skool

@ancipital 4 ай бұрын

Rather than soldering it all on - did you think about doing it all with wirewrapping techniques? I've not tried this myself (yet!) for anything though could be entertaining to give it a go. Also makes it easier to fix mistakes. I remember the first minicomputer I worked on (DEC VAX 8600), if you looked in the back, the whole backplane was wirewrapped!

@DrMattRegan 4 ай бұрын

Yeah, I've tried wire-wrap in the past, but i actually prefer point to point soldering. I find wire-wrap (for me) to be slow. I learned to do this back in the day, when wire wrap sockets were expensive. Also i want to put it in a spectrum case.

@ancipital 4 ай бұрын

@@DrMattRegan Understandable going into a spectrum case, no room for wirewrapped. Good video though so thanks for the interesting start to finish of getting that working.

@akkudakkupl 4 ай бұрын

This might end up being a better ZX Spectrum than the original ;-)

@DrMattRegan 4 ай бұрын

At least it won’t use annoying ULA

@alanclarke4646 4 ай бұрын

VGA output and no "dot crawl". That alone makes it better😊

@fredimachadonet 4 ай бұрын

This is awesome! Would it be possible to share the Arduino and C++ code to generate the video via USB? I wanted to do something similar with the TRS-80 Model 3 clone that I'm building, specially because I don't know how to build the video circuit.

@DrMattRegan 4 ай бұрын

Yep, i'll make mention of it in the next video.

@GregCoonrod 4 ай бұрын

Just out of curiosity, why do point to point soldering instead of wire wrap?

@DrMattRegan 4 ай бұрын

I always found wire-wrap a bit cumbersome and slow. I find this technique easier myself.

@alexloktionoff6833 3 ай бұрын

Could it be simpler to have two SRAM chips, probably even 3: 0 - ZX RAM 1 - pixels buffer 2 - attributes buffer? Clearly separate XZ ROM+RAM from Video and just use WAIT when Z80 writes into video memory. Even adding 1 or 2 SRAM chips could reduce total chips count, assembly and debugging?

@DrMattRegan 3 ай бұрын

At some point, the memory storing the video data to displayed needs two paths into it, one from the CPU and one from the raster generator. Other than dual ported memory or VRAM, we are going to need some sort of multiplexing on the address lines, and this is where many of the chips are.

@zxspectrum16KB 3 ай бұрын

If u can get video ram without contention running on zx spectrum try some freescape titles they were very slow can u overclok the cpu to 16mhz and 32mhz? Try adding ula+ support or spectra + ulax?vdac2?

@DrMattRegan 3 ай бұрын

Interesting, will look into it when i get a chence.

@zxspectrum16KB 3 ай бұрын

@@DrMattRegan please do

@ESPArduinoIDE 4 ай бұрын

I've always wondered why the authors of the clones didn't do this right away? Great job!

@DrMattRegan 4 ай бұрын

Thanks. Yes, Superfo uses a second SRAM for storing the video. I still haven't to get it to work at speed yet (still working on the VGA output), but for the moment, the 74HC374 seems to do the trick.

@nickmoore385 4 ай бұрын

That makes sense now. I was wondering what the second RAM chip was for on his ZX-128- Max design.

@peddersoldchap 4 ай бұрын

Would it be possible to use this EPROM to replace the ULA on a real Spectrum? PS - I'm not that experienced with electronics, but I know how to solder and use a multimeter. And do basic circuit calculations.

@DrMattRegan 4 ай бұрын

No not really. This design uses SRAM, while the spectrum uses DRAM

@peddersoldchap 4 ай бұрын

@@DrMattRegan Would it be possible to adapt the design?

@_wave64_ 4 ай бұрын

Can you share what wire and insulating you're using?

@DrMattRegan 4 ай бұрын

So this is the exact wire i use www.jaycar.com.au/blue-wire-wrap-wire-on-spool/p/WW4346?pos=1&queryId=5bf58702e3ae70ed5bcbb145f0e4f3ef It's from a local retailer, but it is kynar brand, you should be able to find it on ebay.

@alexloktionoff6833 4 ай бұрын

Is it possible to isolate Z80 A & D buses with just 10k resistors like in original ZX?

@DrMattRegan 4 ай бұрын

Yep, should be possible to use resistors, but you still need the 74HC374.