tomdehavas
I have been doing electronics since 1972, I built my first computer from a kit in 1979 (UK101) and have been writing software and designing hardware ever since.
Today it's so easy to run up an electronic circuit simulator and a CPU emulator and a bunch of other stuff on your PC but its like the difference between seeing a photo of Saturn and looking at it through your own telescope.
The A5 is not a micro-computer
Although I am using retro components with tenth inch pin spacing that are still in production, for most of the A5 - it is not a micro-computer. The priority is to use understandable components throughout and 2 layer PCBs where you can see what connects to what. There are extensive annotations on the PCBs to guide you. All data sheets for every part used will be supplied as on-line PDFs for you to download. Similarly for the manual and instructions.
The A5 is a learning bridge from electronics to computing
On the www you can find plenty on basic logic gates namely AND, OR, ExclusiveOR and NOT, and the electronics behind them. I will provide links to websites that explain them or I will provide pages to do the job. On the web you can find out how logic gates can be used to build flip-flops and then counters and registers which is wonderful but how do you actually build a working CPU and computer from these components?
That is the gap the A5 bridges and with it, it introduces you to some modern concepts like RISC processor design.
24-Bit RISC CPU
I don't use a black box plug in standard CPUs like a 6502 or a Z80, but rather we build the 24-bit CPU together which has a transparent, elegant and simple yet powerful (ARM inspired) instruction set which can be seen here https://a5computer.com/code/code.html that's why it's a minimal mini-computer. Almost "retro squared" in that it is evocative of things like a PDP-10 or other computers of that time, yet its RISC with no microcode.
The big focus of this project has been understandability. It's not a high performance processor but I suspect it will beat an old 6502 when running at full speed.
The cost and your help for me to carry on with the A5
So far I have spent over 1200 hours on this project (I log my time) and I have enjoyed 99% of it. I want to spend another 1200 hours on it over the next year to finish the VGA board, a keyboard and an on-board assembler editor plus other stuff.
To make that happen, I am launching a Kickstarter campaign to offer the current A5 to backers, going live in mid-October. I have to say that programming with the switches and LEDs is a valuable learning process but it will be fun to make a retro game when the VGA arrives in a year.