[Coco] 6 Chip 6809 Computer

[Kip Koon]

Hi 6 Chip 6809 Computer Enthusiasts,
I have changed the schematic to include the 48-pin Kipper Bus which increased the PCB dimensions to 3" x 3.24".  I just resubmitted the PCB design file to again be priced for fabrication.  I have priced all other parts, so this is the last price component needed to determine the final price for this PCB.  As soon as I get a response back, I'll let you guys know what the price will be.  
In the meantime, here is a first look at the schematic and PCB layout of my version of Grant Searle's 6 Chip 6809 Computer.  Here is the link to my dropbox for the schematic, 
https://www.dropbox.com/s/garhocp0xswvlu7/Grant%27s%206-Chip%206809%20Computer%20-%20Exactly%20Like%20The%20Original%20Design%20tighter%20layout%20sch.pdf?dl=0
the PCB layout,
https://www.dropbox.com/s/44mkgaa1sdzh7a8/Grant%27s%206-Chip%206809%20Computer%20-%20Exactly%20Like%20The%20Original%20Design%20tighter%20layout%20brd%20no%20traces.pdf?dl=0
and the parts list.
https://www.dropbox.com/s/vx9p0d914k50rf7/Grant%27s%206-Chip%206809%20Computer%20-%20Exactly%20Like%20The%20Original%20Design%20tighter%20layout%20Partslist.txt?dl=0
Since Grant's web page has all the details, I will not be repeating all details here.  I will cite a few important points however.
I have augmented Grants design with a few changes of my own so here is a link to Grant's original design for the 6 Chip 6809 Computer.  His original schematic for the project is found there as well as all explanations.
http://searle.hostei.com/grant/6809/Simple6809.html
This single board computer (SBC) supports the use of either the Motorola MC68B09P or the Hitachi HD63B09P or HD63C09P microprocessor chips.  
WARNING: NO "E" versions of either processors can be used on this PCB.  THE PINOUTS ARE DIFFERENT!!!
I added a green power led, reset and halt pushbuttons with associated red LEDs, and 1K resistors on all interrupt inputs to the processor to allow each input to be used in a custom circuit by the user.  In the original design, they were all tied high.
The BA and BS outputs indicate the current state of the processor and are found on the Kipper Bus.  Early on, I thought it would be cool to "SEE" the processor state on the fly, so I put LEDs on both the BA and BS outputs in the schematic, but since I have been readying this circuit for production and not having found any maximum drive current rating for neither the BA nor the BS outputs (unless I over looked it in the processors' respective datasheets) I will be eliminating these two LEDs.  I used 74LS244/74LS245 buffer chips when I initially breadboarded this circuit 4 years ago to give me all the LED indicators you see on my wiki page thinking I would be breadboarding further expansion circuits.  
All processor signals are available on the Kipper Bus.  WARNING:  There is NO BUFFERING of any signals from the microprocessor.  The use of any outputs from the processor on the Kipper Bus by the experimenter needs to have a buffer chip to protect the cpu.  This is the responsibility of the experimenter.
NOTE: Since this 6 Chip 6809 computer is a minimal 6809 SBC implementation, it has only 32KB of ram, so bringing up NitrOS-9 of any kind is not possible.  A more capable SBC implementation is required to run NitrOS-9, even Level 1.  That doesn't mean you can experiment though.  :)
The custom modified Microsoft Extended Basic is contained in a 16KB eprom.  The actual code is approximately 9KB so that leaves about 7KB of eprom space free.  Maybe there is room for code to add some rudimentary floppy drive, IDE hard drive, CF or SD Card storage routines.  It couldn't be a fully implemented DOS, but maybe enough to play.  I'll leave this possible option up to more experienced software engineers on our list.  Any additional required hardware for this function can be added at a later date.  
I have several modified versions of this 6 chip 6809 computer on my wiki page showing various stages of design with the I/O space moved from $A000-$BFFF to the end of memory leaving room for about 56KB of ram.  See my wiki page for further information.  The changes in each version show the progress I made toward a better SBC that I wanted to someday make.
Initially, I felt this first version of the 6 chip 6809 computer was too restrictive especially with only 32KB of ram,  therefore I was going to release it without any expansion connector whatsoever plus it was not in Grant's design, but at the request of a few people, I went ahead and added the 48-pin Kipper Bus connector to facilitate expansion with your custom circuits.  I will of course entertain any needed/wanted changes.  I recommend that we start small at first and work up from there.
As always positive suggestions and corrections are most welcome.  Thank you for your time and interest in this project.  Take care my friends.

Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon