If you can get A15 without a blue wire, it does not seem that you would need the new select signal based on /BANK6. Requests for 8000 to 9FFF appear to already go to Bank 3, so you'd just need to detect addresses in that range in the OPTION ROM. It looks like the service manual schematic for bank select does that using NOT( A15 AND (A14 OR A13) ).
—b9 On Mon, May 16, 2022 at 3:57 PM Stephen Adolph <twospru...@gmail.com> wrote: > I took a fresh look at the T200 "all ram mode" which would be needed for > REXCPM to work (nicely). > Summary: it is actually feasible I believe to implement an all RAM mode > fairly easily, which would support CP/M nicely. > > *Issue 1. The 8k ROM at 8000-9FFF* > * as shown on the schematic, the M15 ROM is only enabled when /BANK1 is > low and A15 is high. > (also reference the 8k rom datasheet in the tech reference manual) > * also as shown on the schematic, the M13 32k ROM is only enabled when > /BANK1 is low and A15 is low. > > *SO - the 8k range is only active in /BANK1.* > > *Issue 2. Creating an all RAM mode* > * /BANK3 enables the option ROM socket for 0000-7FFF address range > * /BANK6 enables the 2nd option RAM socket for A000-FFFF address range. > * a new select signal is needed for when /BANK3 = 0 (option rom selected) > AND A15=1 (upper addresses) AND /BANK6=0 > (so when we are using the option ROM, and address is in range > 8000-9FFF) > > * A15 is available in the OPTION ROM socket indirectly; as shown in the > service manual in Figure 4-3, the AD bus is provided to the option ROM > socket, as is ALE. This means that A15 is present on AD7 (D7) on the > falling edge of ALE. > > *SO - by stealing /BANK6 from the 2nd Option RAM socket, REXCPM could be > programmed to provide an all RAM mode.* > > *What's needed to make REXCPM support T200* > > 1. A modified REXCPM that is able to deduce when to enable RAM in the > 8000-9FFF range. > 2. an Adapter Board sitting in Option RAM #2, which sends 3 signals to > REXCPM (1) Battery voltage (2) /RD signal and (3) /BANK6 signal. > 3. an updated RXCMGR application > 4. an updated "T200 CP/M" IE the M100 CP/M modified to use the T200 > environment. > 5. updated CP/M uilities > 6. (VirtualT updated to support REXCPM for T200...) > > > > > > > On Sun, May 15, 2022 at 5:35 PM Stephen Adolph <twospru...@gmail.com> > wrote: > >> There would have to be a convenient plug and play ideally way to decode >> that. >> From what is present in the ram module compartment, I dont see a good >> solution. >> I'll take another look. >> >> On Sunday, May 15, 2022, B 9 <hacke...@gmail.com> wrote: >> >>> I, too, would love to see RexCPM for the Tandy 200. >>> >>> I apologize for my ignorance, but why is there a hole? For ROM? Would it >>> be possible to bank out 8000 to 9FFF and replace it with RAM when running >>> CPM? >>> >>> —B9 >>> >>> >>> On Sun, May 15, 2022 at 9:44 AM Stephen Adolph <twospru...@gmail.com> >>> wrote: >>> >>>> Hi >>>> >>>> At this time, no. It would require some changes due to the unique >>>> memory map in the T200 relative to the M100. >>>> >>>> I think the biggest issue is that an all ram mode is not clearly >>>> possible. There would be a hole fro. 8000 to 9FFF. That's not great for >>>> CPM. >>>> >>>> Steve >>>> >>>> On Saturday, May 14, 2022, Hiraghm <hira...@hotmail.com> wrote: >>>> >>>>> Is there an equivalent to the Model 100 REXCPM rom for the Model 200? >>>>> >>>>> >>>>>
