And now for something completely different, not only do I take an enormous amount of time to do something, I also overrun myself with different projects...

After a year or so of designing PCBs and sending them for fabrication, I finally decided to go for the big one and design a full Eurocard (160x100mm) computer. I have enough confidence on my EDA package (gEDA) and myself to design it, and the prices are also relatively low for a double sided board so I'm jumping to it.

When I dismantled the breadboard mini85 I promised to do a PCB version (this was in 2008!), so here I am back on it 4 years and 2 kids later!
The idea is about the same, build a minimally usable CP/M system on a eurocard, with standard TTL logic circuits, minimum I/O, a switching power supply for the computer and the drive, which is a 3.5inch floppy on top using the high density (1.44Mb).

I've been scaling down from the initial idea of having 512k of SRAM and a paging arrangement and a 8256AH as a UART and parallel port (like my 68k project... that, by the way, is also on hold...), and slowly going back to the simple original Mini85.

I even had a port for system configuration and dip switches, but this version (below) no longer has a MMU.

I think that I am finally setting for a 8085 at 8Mhz connected to a upd765 and a software UART with SID, SOD and RST5.5 lines, memory will probably be 64K SRAM (w/ 32K paged in/out) and a 32k ROM. An ON/OFF switch, a RESET, a TRAP and a RST7.5 interrupt push switches.


Roman said...

Hi, it is really very interesting project. Will you make more boards ?

Unknown said...

Yes, that's the idea. But I'm still drawing the schematics. I know I'll have some problems fitting everything in a Eurocard... but that's another story... (google ZetaSBC for a similar project)

Tom McLeod said...

can't wait to see more on this!

Tom McLeod said...

can't wait to see more of this!

Unknown said...

Thanks Tom,
currently, I'm away from home and I have another project due in October. We're already in mode "all hands on deck" for this one so the mini85 will wait a bit more... Sorry..
my projects always take ages, but they usually end up pretty fine :-)
Thanks for stopping by.