Follow up: Great news! I had an old guy eureka moment! So, 5MHz on T102 is pretty well baked and optimized, but an easy upgrade for M100 was eluding me. The main issue: The internal stock SRAM is slowed down by the A* signal, which drives the chip selects from signals /RD and /WR late in the machine cycle. This leaves little time for the SRAM to react.
The eureka ... pull A* high. This frees up the chip selects to be driven solely by IO/M and address lines, which opens up the timing window substantially! So, the M100 5MHz upgrade just got a whole lot easier. The stock SRAM works at 5MHz by making this one change. I will be now documenting my 5MHz upgrade for M100 and I am pleased that it is even simpler than T102. For the hardware keeners - take a look; the SRAM chip select circuitry works perfectly well with A* pinned high. ..Steve On Wed, Nov 17, 2021 at 9:55 PM Stephen Adolph <[email protected]> wrote: > 2x; very much noticeable. I'll have to do a video or something. > > The screen io is 2x faster. It is fed through the PIO chip which is > running in step with the cpu. > > In order to keep the serial port running at expected rates, the timer > portion of the PIO needs a 2.5 MHz clock though. > > To keep software compatibility, it makes sense to keep the serial port > running at the correct rate. > > Last comment: in my speed tests last year I found I could speed things up > quite a bit faster than 5 MHz..maybe 8MHz, until the screen finally halts > the machine. So the LCD is the ultimate bottleneck. 5 seems comfortable. > > > On Wed, Nov 17, 2021 at 9:17 PM John R. Hogerhuis <[email protected]> > wrote: > >> Congrats that's a really cool mod. >> >> How does the screen scrolling seem with this mod? Faster? >> >> -- John. >> >
