I was never really gone, but I should be able to get more videos out over the next few months. I have the broad strokes of a plan for the rest of this year.

Glad you are enjoying them!

You are welcome! Glad you are finding them interesting.

Glad you enjoyed it! There will be more frequent videos over the the next couple of months.

Making the expansion the main port rather than the rom cartridge would of course be easier. I’m not the guy for the easy path.

Flux is sometimes a tradeoff between easier soldering and the mess!

@@weirdboyjim That's certainly true! I've spent plenty of time cleaning up leftover flux with alcohol and a close-cropped brush. Situational for sure, might help enough to be worth the mess on something like this edge connector. Love your videos, inspired me to implement a close analogue in verilog to run in simulations to really understand what's happening at the lowest level of CPUs.

I know how you feel. There is a bunch of old kit from my youth I’d love to look at again but I have no idea what happened to it.

Well you're right, I didn't consider that. Doesn't really matter for a temporary breakout like this but I'll try to keep it in mind when I design something more permanent with an edge connector.

@@weirdboyjim Hehe! Just trying to save you a mistake I've made before!

You are welcome!

Thanks! Hope it satisfied, Next video won't be as long in the making.

Sounds interesting!

Hope you enjoyed it!

Thanks!

Did you have any carts for it or did you just use it as a joystick interface?

You can always tell the stuff I made with by all the lights!

I’m equal parts impressed and terrified by that description. Cool that it worked!

Interesting! I never had significant hands on with the msx.

Thanks Pete, was never really gone but there should be more regular videos again.

Yeah! That was handy! The spectrum basic is an odd beast, the method of typing whole keywords seems weird at first but once you realize that's how it's tokenized in memory (rather than being stored as text) it makes much more sense.

They've spelt the "refresh" signal name incorrectly though - it should be RFSH not RFHS.

@@TomStorey96 I’m prepared to overlook that.

Thanks! I like to think young me would be impressed by old me making this work!

Perhaps, but then I would be reading lots of comments about how I shouldn’t use the auto router 🤣. Glad you liked it.

Well the cartridge port isn't anything like as flexible as the snes one was, but part of my goal is to push the limits of what we can do with it.

The Spectrum has bitmapped memory in RAM. The NES used a tile table located in the cart, usually ROM. So that's how mappers could do tricks like that. For the Spectrum you can only alter the screen by reading and writing to the RAM. Even if you had some separate circuit, rather that doing it on the CPU with software, you're still limited by how quickly you can write to old RAM chips like that. So that idea would be difficult to get up and working, at least much more difficult than on the NES. The tiles in cart ROM meant the NES didn't need tile RAM, so was quite a lot cheaper to make. The downside was that each cart needed 2 separate ROM chips, CODE for the CPU, and CHAR for the PPU. They had their own bus each which is why the NES's cart connector was so enormous. Overall it was cheap, and made games at least twice as expensive as they had to be for other consoles. The Master System did it the usual way, and had much better graphics, so there was no advantage to the design other than money. "NES-expensive" is a term that should be in the lexicon as much as "Nintendo-hard" is! ALL 8-bit systems had difficult games, it's not a Nintendo thing. But as ever, it's how the Americans had things, and they're in charge of the language apparently, including slang. See also the "Videogame Crash" which only happened in North America, and only affected consoles.

@@greenaum yep I’m aware of how the spectrum worked - I wrote enough software for it 🤣 I’ve also written an NES emulator along with others in my spare time… Although different there is the possibility of greatly increasing the potential using a custom cart: DMA transfers. By halting the Z80 and copying from ram in the cart to display ram which is much faster than the usual method of popping from the stack into registers then pushing into display RAM. Handling sprites and a tile map based display in the cartridge which will be pushed to the display ram without the need for the z80. Other effects such as pixel scrolling etc which again would be handled in the cartridge and then DMA’d to the display ram. Yep it’s different but there are. A lot of possibilities 🤣

Yeah, the clock is a basic 2 transistor oscillator. Looks like the ULA pulls it down when it wants to take over the bus.

All my education was computer science. We didn't touch on any circuitry stuff but there was some logic / gate theory.

@@weirdboyjimThat's great passion of you to work on H/W... I am admired ...

Yeah, I remember the lower ram was slower.

It was with the ZX, messing with some game in MONS (as one does), that I encountered my first anti-debug feature ever... I was staring at the screen in disbelief at the code writing a constant into a register, then immediately reading it back and comparing it to another value - wtf, how can this ever succeed...? Then the little lightbulb went on above my head and I just laughed my ass off: the register in question was the R-register, which gets auto-stepped in hardware, and if you were step-by-step debugging you sure as hell didn't read the same value back as if the code was executing continuously. Trivial to bypass once one understood what was actually supposed to happen...

@@AttilaAsztalos Ah, yes. That was the second version of something which I think was called "Speedlock". I wound writing a program that automated the process of modding the decoder to get to the loader. Ended up that I could crack those in a few minutes!

Interesting, and a bit weird. Good to know I was seeing legitimate writes though thanks.

When I was kid I had this crazy idea of using the audio cables you used to save / load to audio cassette to network two spectrum together. Possible but it would have taken up all the cpu's focus to either send of receive.

If only I knew the basics of digital electronics then!

@@weirdboyjimI`m sure I read in the ZX manual when I was a kid that the IN OUT functions were controlling the interface pins. I might have to have a utube search. Would of been nice to know what we know now. I was just playing with Triacs etc making disco lights with a 555 timer and old tape desks. I used a decade counter chip to switch between lights. Then add ZZTops lol.

That sounds very likely. I now have to choose between doing a web search or opening it up and getting the oscilloscope out to confirm ;-)

That would probably be smart and safer, we do if course always do the smart and safer thing 😅

Actually an interesting challenge when you stop and think about what is involved.

@@weirdboyjimSome of the Basic compilers for the Speccy had it too. Such a luxury! Many was the time when as a kid I had to manually go through changing all the line numbers (-:

I may look into that, someone posted a code sniper that implies it’s not enough

Unfortunately that would be a problem for the edge connector the other side. I wondering how think I can go, I have a similar problem to solve elsewhere that idea may be more suitable for.

@@weirdboyjim Just by watching the video I think you can get away with 1.8mm

Glad you liked! No, these are very distinct projects. I used the UART for this as it was just more interesting to connect something I built myself than show led’s lighting up!

I’ll take a closer look next time I have it out.

I have to admit I was under time pressure when I made this board or I might have been a bit neater in a bunch of areas. If I had known how much of a pain it would be in both wiring and video editing I'd have put a bit more work into the PCB.

That appeared on my phone notifications as "Babe... hurry up and get home.", worrying for a second!

@@weirdboyjim 😬😬 oops. Sorry james.. didnt mean to worry you!!!

Working on it or interfacing it to the spectrum? That would be pretty much just a wire swap from here.

@@weirdboyjim both! 🙂

@@FrankGevaerts Comet o think of it, interfacing it is the easy bit. Making some code to play music on the spectrum would be time consuming. Maybe I should just work on the Audio circuit.

@@weirdboyjim Maybe... I'll admit that my motivation is that I want to do this myself (although maybe on an RC2014 instead, or both, as I have an RC2014 backplane with Spectrum edge connector...), so you finishing the audio circuit far enough to publish everything would help :)

@@weirdboyjim I think getting the audio onto a PCB next would indeed be great!

I'm using memory writes rather than I/O ports because at least some the lines I need are exposed in the cartridge. There is some really weird stuff in the IO range of the spectrum that was done to save cost that I didn't want to fight.

You could definitely use that to tin the pcb but I’d be worried about taking hot air to the plastic of the connector.

Why do you think that might be needed? The computer just worked without anything plugged into the expansion port.

@@weirdboyjim because the computer didnt care about reading an osilloscope? I guess

Perhaps my wording was poor. I always had a set of pins that had every output from the expansion port in the order they appear on the edge connector (That was easy to route). The bit I removed was an extra set of address and data lines that were reordered numericaly (That was would have been difficult to route as many lines swap over). In hindsight I wish I had spent the time to route the extra set, it would have made the testing step smoother.

I went back. You installed pin headers in the through holes of the middle edge connector socket.

V2 in the works? 😁

I think you are right. I should have tinned the board and the connector. Maybe tried to shape them beforehand as well.

Yes, that’s the way I do it, it’s a lot more consistent than just putting the solder on the top.

I know some people don’t understand people playing with retro tech.

@@weirdboyjim Back in the day I hooked my 48k up to a line printer and wrote a program to calculate Pi - outputting to the printer, it went through a box of tractor fed paper. I also made a UPS as I was forever forgetting to save my listing. The last project I made controlled the ignition of my Dads car and heated up the interior for a warm journey to school. I have moved on to the ESP32 range of boards now as they have a lot more power and versatility and a lower cost of entry!

I had no idea you could mess with it like that. I assume that's partially a by product of the way video memory is shared.

@@weirdboyjim The lower 16K is refreshed by the ula, the upper 32K by the Z80. You can not run this trick in the upper 32K because the program is fading away.

@@weirdboyjim bit 7 of the R register can be used as a "general purpose output" - the Z80 auto increments R each instruction but it wraps back to 0 after 7F rather than FF. You can manually set/clear bit 7 and by decoding the refresh cycle you can then latch it into a flip flop or similar.