Final story on 8MHz (well final for now!). Actually, the processor/ram/keyboard all work at 8MHz. Only one thing I can see, and it is pretty important, doesn't. The LCD. The driver chips have to communicate with the CPU, and they are just too slow to get their data on the bus in time. So, I think that's the end of the story; no clear way to improve on the Driver response time.
6.144MHz is exactly 2.5x nominal clock rate. That seems to be achievable. On Sat, Oct 31, 2020 at 7:12 PM Stephen Adolph <[email protected]> wrote: > On Sat, Oct 31, 2020 at 5:52 PM Joe Grubbs <[email protected]> wrote: > >> Aww yeah! I'm liking where this is going. Will the sluggish original ROM >> handle 8Mhz+? >> > > No, for sure not. Right now I have a 120nsec EEPROM in the socket and it > supports 6.2 MHz. > If I simply place the original ROM back in - no go. > But the Main ROM is the easiest thing to replace. It is already > socketed! There are many ways to address it. > > So far here are the changes to run 6.2 MHz (my current setup) > 1) you need a faster CPU + crystal. I'm making a board for that. Which > CPU - TBD. There are a few choices. (I really should try the stock CPU > and see how fast it really is. I am currently using the 8MHz Tundra 80C85 > CPU) > 2) you need faster RAM. You could use REXCPM to solve that problem. > Otherwise... a lot of soldering work! > 3) faster main ROM. Teeprom would be a good solution here. > 4) improved M2. stock = TC40H245 (good to 5MHz). I have piggybacked > 74HC245 (6MHz) > > I'm puzzled by what is failing to work at 8.2 MHz. Everything so far > looks ok. I'll keep poking around.... > > > > >>
