I recently had the chance to buy a Stellation Two "THE MILL" 6809 card on ebay (the collectors "sancta santorum"!) and install it in my Apple II+ .
The "The Mill" card from "Stellation Two" company is a co-processor card that uses a 1 MHz 6809E and enables execution of Motorola 6809 cpu code in Apple II computer series while sharing the bus, memory, peripherals and clock with the 6502 cpu so that both processors are kept running at the same time, the 6809e running at 100% speed and the 6502 let working in the 6809E dead cycles for the remaining 20% time.
The card was sold in 1982 at a retail price of $369 and included a "Pascal Speedup Kit" disk and a demo disk with some software to show the 6502/6809 interaction capabilities.
This should be the picture of the original package
The most interesting feature of this card was that it offered the option to buy an OS/9 kit to let OS/9 operating system run in the Apple II.
OS/9, created by Microware Systems Corporation was a rather advanced operating system for those times and it's still popular in today's embedded systems.
The OS/9 version offered by Stellation Two is known as "Level One" and its main feature is that it's a realtime OS that allows execution of multiple programs at the same time, something "stellar" for an Apple II.
The kit consisted of the OS/9 operating system on Apple II formatted 140K floppy disks and a daughter board to be installed piggiback to the "The Mill" card.
Unfortunately "The Mill" cards equipped with a daughterboard are extremely rare; as far as I know, just one was sold on ebay in the last few years and it was part of a combo whose price skyrocketed to $1525.
I simply could't afford it and the daughter board does'nt look original!
The appetite for OS/9 was too much so I started digging for those faint, rare, scattered pieces of information about the inner working of the original daughter board; I had to proceed by elimination because much of the available information is wrong, unproven or incomplete.
After a coulple of months of real obsession I had enough knowledge to attempt to build a (functional) replica of the original daughter board.
I spent 3 days designing, programming and pcb etching and here is the result
My The Mill card now runs OS/9 !
It's not been a trivial task because of the lack of information and also due to the fact that a lot of OS/9 disk images that are published on the internet are broken.
Now I have a fully functional OS/9 machine that I even tested in multitasking with a mating Mountain Computer CPS card, a real "taste" of the mainframes of the '80s.
The "The Mill" card with OS/9 is fully compatible with 80 Col. Videx cards, some parallel printer cards, serial and clock cards and an assembler and editor for 6809 opcodes is available from the content of one disk image that apparently comes originally from Microware and that can be found oline.
I initially experienced Apple II freezing (lock-up) while running OS/9 BASIC09 demos. I later discovered that my clock generator IC on the Apple II motherboard, a 74S175 location B1, was faulty.
It was probably going out of specs with the rising of temperature inside the Apple II case, while not showing any sign of malfunctioning during 6502 only cpu operation.
Probably the tight sharing of the bus by the two processors requires a good stable bus clock.
That's a hardware accomplishment far beyond my own meagre skills. "The Mill" did catch my attention before because my own family stuck to the Radio Shack/Tandy Color Computer line for many years (moving to a Macintosh LC II, pointed by some programs that could get away with copying the MacPaint and MacWrite interfaces, when the unsupported "CoCo" community shrank to the hobbyist stage), and the Color Computers used the 6809 processor... There was always plenty of discussion about getting OS-9 running; you could buy it through Radio Shack. There seemed less discussion about what sort of applications you'd multi-task with it once it was running, but maybe that wasn't part of the game.
The daughterboard is original.
I was referring to this board that was on sale on ebay:
Do You think the daughter board is original? It has no markings and build quality is'nt great;
anyway I have to say that the Stellation TWO OS/9 BASIC09 DOCUMENTATION manual at page " V " says :
As you face the keyboard of your APPLE II, the daughter-
board switch pulled towards you will activate the Pascal
Speed-up Kit and the Assembler APPLE DOS Environment.
Pushed away from you, towards the back of your computer,
the switch activates the OS/9 mode.
This is the description of a switch lever with a forward or backwar position (this last picture) , while the doughter board with the "Stellation TWO" markings has a Up or Down operated switch. Maybe they are both original...
I don't know of any good "FLEX" OS disk image around for the Stellation Two The mill, all those I found require a Seikou EXCEL-9 card.
According to this review published in Year 1980 a "FLEX" implementation should exist for the The Mill
I see that your board is a Rev C and it actually has an additional two chips on it when compared to the Rev B. It's not something that I have noticed before. If you have some time in the future it would be great to compare the difference those two chips make compared to the original circuit diagram in the Mill user manual.
I did email Jim Hinds awhile ago asking about the successor to The Mill, the Vitamill. He discussed that the implementation of the mill was not that great, and that Apple had helped to guide for the later card. Maybe the extra chips helped provide this in the Rev C mill card. I have never seen any picture or any technical detail for the Vitamill. Only some references in the magazines.
I will find the email reply and post here if anyone is interested.
RJUSTICE : I did notice too that REV-C boards carry some extra ICs. I'll take the time to try to understand what's their use.
Here are pictures of two REV-C boards, the first one belongs to Applefritter user jwg1962
I'm certanly interested in any information we could put together about this boards; Rob please post the email if You can and pictures of other boards if You have them.
Congratulations on working out what the daughter card does.
I have one of the Mill cards that I used for the Pascal speedup kit.
I was able to upload the original disks some years ago when the search
Can you give me any details on the daughter card?. I would like to see
OS-9 on my Apple II. I have an ulterior motive: I'm looking for the
source for Dynasoft Pascal what was released for the 6809. I've
lucked out on finding it for the Apple II.
I can etch the PCB if needed.
Today I published the PCB schematics and PLD source files for my daughter board here at github.
There is a Creative Commons Attribution-Non Commercial-ShareAlike 4.0 International Public License applied, so any right is granted to use it but NONE to sell it.
In the next days I'll append some more details to this thread.