The Dr. Neherlab (of the Dutch Telecom, PTT) had in the end of the 70ties their own developed bus system. I was there and have such a (6800)based system still in the attick. My first home-built system, 1978). There were 8k bytes (with 2114) memory cards, 16k (2716) EPROM cards, and *different* CPU cards. I remember the 6800-based (obvious), but there was also a Z80-based card. Keep the memory boards in the backplane, swap the 6800 for the Z80 CPU card, and the system works (with other software of course). To be that versatile, the CPU boards had extra logic to make the bus interface always working (for example, the 6800 is synchronous in the bus transfers). Their system used the DIN41612 connectors (IIRC), It is the same connector used on VME modules, and has 32 pins in one row. With the 2- or 3-row version you have sufficient pins (96) for even a 68000-based bus system. That system also carried the power supply over the bus. I remember that pin #1 and pin #2 and pin #31 and #32 were used for +5V and GND. Hell, why not use the VME 3-HE bus pin designation for you own design? If you want a reliable, robust system, do not use card edge connectors. The VME connectors are superior. Besides, Eurocard boards with at one short edge drilled holes for DIN41612 3-row is pretty standard stuff. And if you want to build a small system, and have "dedicated" card for memory, (flash)ROM, and do not forget I/O !! - my humble opinion is Eurocard is the best choice. BTW, the female 3-row counterpart for DIN41612 also exists in a version to connect to flat cable! So, take some 20 cm of flat cable and pinch that female part on the flat cable, et voil?, you have the backplane / bus ! For improved noise immunity perhaps not the best solution, but then it is fairly cheap that way. my 2 (euro)cents, - Henk, PA8PDP. ________________________________ Van: cctalk-bounces at classiccmp.org namens Roger Merchberger Verzonden: di 13-12-2005 19:03 Aan: General Discussion: On-Topic and Off-Topic Posts Onderwerp: Re: CUBIX/6809 updates Warning: I did not top post! There are further responses inline with the reply. ;-) =-=-=-=-= Firstly, I'd like to mention that I've always wanted to build my own homebrew 6809 system... altho I've been thinking of designing my own buss system (around 80 pins or so) so other CPUs could be used if desired. I was thinking of a multi-board system with a 6-7 socket backplane. I want it to be educational to others (read: see-thru Lucite case & lotsa Blinkenlights! ;-) at the same time that I learn from it, too. For a few reasons, S100 is not an option: I want the system smaller / easily portable (I'm guesstimating in inches: 6x6x9, with an external 5V only switcher), and I also want it to be easily buildable by a hobbyist. Trying to dremel an S100 cardedge would seem to be quite a bit of work for not a lot of gain - but square boards with a pair of 40-pin IDE connector (for example) edge-soldered on would be pretty easy to do at home. I do have a question: Are there any 80-100 pin buss structures already in use I could copy that might fit my bill? I'd rather do something that might be compatible with something else out there if it's similar enough to what I want to accomplish. I'm hoping to take lots of pictures & basically make the design free on the web as I do this, mainly to show people if an idiot like me can make a computer, so can you! ;-) Oh, and for the record: Cubix looks *kewl*. ;-) Rumor has it that Scott Stevens may have mentioned these words: And it's never too late for good ideas. ;-) Them's fightin' words. 64K w/OS-9 got me thru High school & my first year of college, before I got my CoCo3 & 128K (later to 512K) but I still had a maximum 64K code space - and that kept me working until the mid-90's. Other than running (crawling) Autocad, my '386 was the 'toy' and my CoCo was the workhorse. Once I got an EISA 486-66 server from my (then current) employer, did I consider the CoCo my secondary machine. Unless you're running Windows. ;-) A few of those microcontrollers have 128K of flash on 'em now. I want my CoCo on a chip! ;-) Laterz, Roger "Merch" Merchberger -- Roger "Merch" Merchberger | "Profile, don't speculate." SysAdmin, Iceberg Computers | Daniel J. Bernstein zmerch at 30below.com | This message and attachment(s) are intended solely for the use of the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution, or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a "reply" message. Thank you for your cooperation.