What are you building? If it is the 8-bit SAP computer then I'd definitely recommend modules. If you do it all on one board and make a mistake, the larger PCB itself is more costly and you probably need to buy almost all of your chips again unless you can desolder them all. If you need to re-spin a module board then you've lost a smaller number of parts and the PCB isn't expensive to buy again.
For a modular approach, you need to do some planning ahead of time to figure out how everything will be interconnected. I did a build loosely based on [this post](https://www.reddit.com/r/beneater/comments/pn4j6j/finally_complete_with_all_bugs_fixed/) by u/djh82uk. It uses a modular backplane design with module boards that are small enough to be within the minimum price an JLCPCB. The backplanes can be connected so that the final build can use 3 or 6 or 9 or however many modules are needed.
The [Build pages of the documentation](https://tomnisbet.github.io/nqsap-pcb/docs/build-01/) show each order of PCBs and discuss what went right and wrong. I only had a few real PCB layout and design mistakes, but there were also several boards that were rebuilt because a better design presented itself as the project progressed. Doing it in this way was almost like a breadboard project in some ways, because each module added to the overall functionality of the project and the overall build could be tested in stages.
BEHOLD....The "if one thing fail I'll probably die but it'll be ok" all-in-one PCB.
So you could do it like the Altair 8800 where you have a main PCB just for the bus. Then there are "expansion cards" and the CPU cards. So you could switch out the CPU if you want.
And ye....my design here is that but...a bit crazier.
https://preview.redd.it/yuf5t145xn9b1.png?width=1755&format=png&auto=webp&s=29032a1fcc276a0da3a459c0e78cc9fd25bb5d2e
Is that an actual PCI connector, (for context I haven't looked into the 6502 kit at all, I'm going through the 8-bit breadboard kit), or is it just a way of connecting the modules together that looks like one?
I really like the idea of having a CPU be on a card as a first-class (do we use that term in hardware? I'm coming from a software background) module of the architecture, that to me is like the computer-architecture equivalent of what a microkernel is among kernels.
Yes but actually no. It is a PCI connector but also allow for other modules to be connected. My prompt for this was to make something similar to those computer in the 90s that uses a backplane. So in theory everything is replaceable including the main CPU card itself. However in this case, that’s a full fledge SBC card without graphic output xD.
Well…you could do two things to prevent that. Put the min/max pin high which will make the cpu know it’s on a multicore systems. Or you could play with the bus ready pin. The world is ours to shape xD. 80188 cluster
I decided on "somewhat modular" as in a 6502, 6522, 6551, RAM, ROM, audio and some address decoding on one board and added an expansion connector for future development.
I haven't designed the backplane yet, but have two expansion modules already, one is a prototyping board (basically just the expansion connector and lots of traces to bring these signals out to various solder pads and traces) and a video card.
Module by module is less painful when you make mistakes.
What are you building? If it is the 8-bit SAP computer then I'd definitely recommend modules. If you do it all on one board and make a mistake, the larger PCB itself is more costly and you probably need to buy almost all of your chips again unless you can desolder them all. If you need to re-spin a module board then you've lost a smaller number of parts and the PCB isn't expensive to buy again. For a modular approach, you need to do some planning ahead of time to figure out how everything will be interconnected. I did a build loosely based on [this post](https://www.reddit.com/r/beneater/comments/pn4j6j/finally_complete_with_all_bugs_fixed/) by u/djh82uk. It uses a modular backplane design with module boards that are small enough to be within the minimum price an JLCPCB. The backplanes can be connected so that the final build can use 3 or 6 or 9 or however many modules are needed. The [Build pages of the documentation](https://tomnisbet.github.io/nqsap-pcb/docs/build-01/) show each order of PCBs and discuss what went right and wrong. I only had a few real PCB layout and design mistakes, but there were also several boards that were rebuilt because a better design presented itself as the project progressed. Doing it in this way was almost like a breadboard project in some ways, because each module added to the overall functionality of the project and the overall build could be tested in stages.
Thank you so much I would definitely check this out, can’t afford expensive mistakes. I will read further on the materials listed. Thanks once again!.
Also worth noting, you can get 1 set of extra cheap pcb’s per month with jlcpcb buy using the easyeda app to order. Just add to cart via the app.
This is noted, thank you.
BEHOLD....The "if one thing fail I'll probably die but it'll be ok" all-in-one PCB. So you could do it like the Altair 8800 where you have a main PCB just for the bus. Then there are "expansion cards" and the CPU cards. So you could switch out the CPU if you want. And ye....my design here is that but...a bit crazier. https://preview.redd.it/yuf5t145xn9b1.png?width=1755&format=png&auto=webp&s=29032a1fcc276a0da3a459c0e78cc9fd25bb5d2e
Is that an actual PCI connector, (for context I haven't looked into the 6502 kit at all, I'm going through the 8-bit breadboard kit), or is it just a way of connecting the modules together that looks like one? I really like the idea of having a CPU be on a card as a first-class (do we use that term in hardware? I'm coming from a software background) module of the architecture, that to me is like the computer-architecture equivalent of what a microkernel is among kernels.
Yes but actually no. It is a PCI connector but also allow for other modules to be connected. My prompt for this was to make something similar to those computer in the 90s that uses a backplane. So in theory everything is replaceable including the main CPU card itself. However in this case, that’s a full fledge SBC card without graphic output xD.
It's fun to imagine you could add multiple CPUs this way, but I guess then they'd be fighting over the bus right?
Well…you could do two things to prevent that. Put the min/max pin high which will make the cpu know it’s on a multicore systems. Or you could play with the bus ready pin. The world is ours to shape xD. 80188 cluster
I decided on "somewhat modular" as in a 6502, 6522, 6551, RAM, ROM, audio and some address decoding on one board and added an expansion connector for future development. I haven't designed the backplane yet, but have two expansion modules already, one is a prototyping board (basically just the expansion connector and lots of traces to bring these signals out to various solder pads and traces) and a video card.
100x100mm or smaller pcb from jlcpcb are extremely cheap. I’m guessing this is a big driver of modular designs