ZX Spectrum build, No ULA.

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.

Part 1: This video

16K ZX81 vs 16K ZX Spectrum

VGA from an EPROM.

Apple 2 wire-by-wire

[alexloktionoff]

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

[andrewkieran]

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!!

[jorgeferreira]

Congrats!
That is a very clever way of sharing the bus with your personal video hardware.
In this days of fast hardware, FPGAs, extra powerfull microcontrolers and massive frameworks, its an almost lost art.
This kind of videos are quite a refresh so I don't totally forget some old tricks.
Thank you for a really interesting and refreshing video.

[AndyGraceMedia]

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.

[mheermance]

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.

[csbluechip]

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

[StratsRUs]

Quality viewing.Warm nostalgia for me.

[vanhetgoor]

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.

[MeeBilt]

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.

[flomojou]

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!

[R.Daneel]

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.

[schrodingerscat]

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.

[kirknelson]

thats some genius level problem solving, enjoying the series 🙂

[nexpro]

Thanks for the vid. It popped up in my yt feed. I swear Youtube 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.

[ESPArduinoIDE]

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

[schmitzbeats]

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.

[ITGuyinaction]

👍👍👍 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.

[sarkasaa]

Well, that subscription was a no-brainer!

[rappzz]

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

[melkiorwiseman]

Very interesting, and it occurred to me after watching this part, that you could add another latch or two to enable you to bank switch part of the RAM (the part which doesn't hold the video memory) to allow the computer to be expanded to run either multiple programs or programs with large amounts of data. Edit: Maybe even simulate a RAM drive for fast loading of programs.