Interesting. I wonder what the original intent of the A* signal was then?
Jeff Birt From: M100 <[email protected]> On Behalf Of Stephen Adolph Sent: Wednesday, April 20, 2022 5:44 PM To: [email protected] Subject: Re: [M100] 5MHz and RAM in M100/T102 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] <mailto:[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] <mailto:[email protected]> > wrote: Congrats that's a really cool mod. How does the screen scrolling seem with this mod? Faster? -- John.
