I've been thinking about it too. /BANK6 is perfect for selecting that ram bank for address A000 to FFFF. No issue.
I believe that , when option rom is selected, it is actually selected for all addresses from 0000 to 9FFF. Now about A15. It is actually present in the socket because the AD bus is present and ALE is present. So all you need is a register to capture it. A15 is AD7 sampled by ALE. The T200 diagrams dont call the bus AD but it is. So, the T200 ram adapter needs to supply 1. Battery voltage 2. /WR 3. /BANK6 (and or BANK5) Three wires, the same as M100 REXCPM but with different logic implemented in the CPLD. For the record, in M100 and T102 REXCPM disables the internal ram by manipulating RAMRST. This isn't necessary for T200. The option rams can be replaced by REXCPM. Back driving RAMRST takes only a few mA. So yeah I think it works. I am thinking about a few little experiments to confirm my suspicions. Still a lot of firmware and software work to do. I already laid out the adapter. That's easy... ;) On Wednesday, May 25, 2022, B 9 <[email protected]> wrote: > 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 <[email protected]> > 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 <[email protected]> >> 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 <[email protected]> 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 <[email protected]> >>>> 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 <[email protected]> wrote: >>>>> >>>>>> Is there an equivalent to the Model 100 REXCPM rom for the Model 200? >>>>>> >>>>>> >>>>>>
