2012-02-27

Mini85v2

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.

5 comments:

Roman said...

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

J Silva 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)

emu_death said...

can't wait to see more on this!

Tom McLeod said...

can't wait to see more of this!

J Silva 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.
JCS