Sounds great Steve, keep us updated on this. You may have mentioned this before, but do the two processors share the bus simultaneously, or is only one or the other (like a Commodore 128)?
________________________________ From: M100 <m100-boun...@lists.bitchin100.com> on behalf of Stephen Adolph <twospru...@gmail.com> Sent: Friday, June 5, 2020 10:44 AM To: m...@bitchin100.com <m...@bitchin100.com> Subject: Re: [M100] dual CPU project Hello all, Interesting update. So, I've been working on getting NSC800 AKA Z80 processor to work in the M100 such that it can be used in CP/M as an alternative processor. Great news is that I now have a solution for actually running the M100 using the NSC800! Not that it really matters; there are no Z80 applications for M100, and the Z80 can't run 8085. But, what this means is that having a Z80 processor for CP/M in M100 is very close to reality. And it is kinda neat to see the good old M100 interface work using a Z80 ;) Learned a lot along the way for how to modify 8085 code to run on NSC800. Also the subtle difference in how NSC800 deals with the Timer driven interrupt TP. More to come, Steve On Fri, May 29, 2020 at 7:46 AM Stephen Adolph <twospru...@gmail.com<mailto:twospru...@gmail.com>> wrote: Reviving this thread. Now that we have a solid CP/M application written in 8080, there should be a way to boot into CP/M using the NSC800. I dropped this project some time back but it is time to revive it, as a processor swap would be a cleaner way to expanding the CP/M application universe for the M100. On Thu, Jul 11, 2019 at 10:30 AM Stephen Adolph <twospru...@gmail.com<mailto:twospru...@gmail.com>> wrote: Motivated by 2 things 1) discovery of the NSC800 Z80 processor that is 80C85 like 2) continuing to work in the direcition of CP/M 3) and recalling that there are 5MHz 80C85 parts out there.. I started to work on a dual CPU card for M100 that enables a couple of things; - standard 2.5MHz 80C85 operation (default) - switchable clock for 80C85, supporting 5MHz - switchable CPU enabling NSC800 at 2.5 MHz. Board is done and heading to the fab. VHDL is mostly done. I don't expect this board will be wildly popular but maybe it has some interest Double speed M100 seems interesting on it's own, let alone being able to support Z80 CP/M applications. Any interest? I have purchased material to make 5 of these. A few more comments. - to install this board you need to remove the 80C85. that's some effort to do - to run at 5MHz you need to upgrade the 81C55 to a 5MHz version. That's also some effort. - NSC800 runs about 5$ on ebay. - fast 80C85 can be had for under 5$. - fast 81C55 can be had for under 5$. - to run at 5MHz you might also find you need a faster main ROM, and faster RAM. TBD on that; will advise after I do some testing.
