http://classiccmp.org/pipermail/cctalk/2010-January/282094.html Is this article available on-line anywhere? Or do you have a reference to it? It sounds as though it might be worth reading. -tony Hi Tony, there are several related articles here: http://mdfs.net/Software/Tube/6809/ Like I said earlier, I am not familiar with the UK microcomputers but when I was researching how to make a 6809 "host processor"/coprocessor it seems like I found several 6809 coprocessor designs. I think Graham Harston frequently posts on comp.os.cpm and he is a hosting the 6809 information related to the BBC and Acorn computers. None of the designs I found were exactly what I was looking for but there was enough ideas that I could cobble together a working prototype. The N8VEM 6809 host processor appears as an ECB 8255 PPI peripheral to the SBC Z80 and as a 6821 PIA peripheral to the 6809. Whether that was a great design or not remains to be seen although it seems to work well enough that Dan got CUBIX ported and I got ASSIST09 and MINIBUG working. Frankly, I think the 8255 PPI strobe and acknowledge handshaking leaves a lot to be desired compared to the 6821 PIA but neither were exactly cooperative IMO. I like 6809 architecture and personally think it was probably the apex of the 8 bit CPUs and (albeit admitted only begrudgingly) better overall than my beloved Z80. Also I think the 6809 hardware is obviously well thought out as it was amazingly easy to get the breadboard systems working. So far the N8VEM 6809 computer has worked great. It hasn't been terribly popular but I made it mostly because I thought it was neat idea. I can see why people like the 6809 so much. Thanks and have a nice day! Andrew Lynch, 73 de N8VEM