Memo-1

In the series "other distracting activities during the heatwave," I looked into the very simple development by a "local guy"—that is, a Frenchman—who created a small computer based on the 6502 processor, with the particularity of being able to connect to the French Minitel. I always appreciate seeing this precursor of networked computing, the Minitel, being put to use. The capabilities of this machine were very limited. The major consequence was that for more than fifteen years, very simple and highly standardized "digital" applications were developed, which enabled French businesses to rapidly increase their efficiency. Imagine: a very simple interface whose learning curve—just a few dozen minutes—was enough to acquire the reflexes needed for a significant boost in usage efficiency. No stress for the user, the "graphical" interface never introduced any uncertainty. And what about security? Point-to-point connections with no possibility of hacking, unless one broke into Transpac distribution points, which were moreover equipped with non-standard hardware to even attempt sniffing a communication. How things have changed. Using Microsoft's online typewriter, um... yes... why not! And will this still be useful with AI?

I suggest you take a quick look at his YouTube page: Memo-1

I grabbed a few screenshots from his YouTube page.

Charming little board, isn't it?

As usual, its format is proprietary. The author took as an example the format of the old cardboard programming cards that were found on virtually all programmable computers of the era, notably the 80-column IBM cards. The problem with all these cards in incompatible formats is that once the board is assembled and tested, well, you put it away and move on... to the next one. As a result, you accumulate these boards and end up forgetting about them. And when you take them out of the drawers again, you still have to find or rediscover the specific connectors, the power supply, the USB-to-serial converter, etc.

So, for the past few months now, I have decided to take the boards I found interesting and remake them in the Euro RACK format. That way, it will "just" be a matter of getting a RACK with a backplane board and a standard power supply, and the boards can be inserted into the available slots, remaining easily accessible at all times, and, of course, stored in the same place. I have always found the TI99/4A's bus expansion system particularly interesting.

Gorgeous!

So I took the MEMO‑1 schematic and redrew it, replacing the expansion connector with a backplane bus connector. I also added a real‑time clock connected to the VIA via the I²C bus, which will need to be implemented using the VIA's I/O ports. This will require some specific programming that can be done later. As for the backplane bus pinout, I adopted the EuroBEEB format, since that system also used a 6502. This results in a board that is fairly easy to build and has a compact form factor.
 

On the original MEMO‑1 system, the expansion connector is designed to accept a cartridge. This will obviously not be possible with the backplane bus. It will therefore be necessary to design another small board that brings the essential signals to the front face of the rack, fitted with a cartridge connector. 

Regarding the Cody computer, which I also mention in this blog, I intend to convert it to a rack format as well. Since Cody has even fewer components, this shouldn't be very difficult, even if I incorporate the USB keyboard adapter.

These two systems, as well as the EuroBEEB board, are all based on the 6502, or its more modern version, still available from the Western Design Center. For now, I have nothing planned based on the Z80 processor, since it is no longer in production. However, since I have used Z80 cores in FPGAs in the past, I might be able to perform the same kind of conversion for Sergey Kiselev's CP/M-compatible board : Easy_z80 .