I'm a little confused. It sounds like you're selecting on /BANK3 = 0 (option ROM selected) AND /BANK6 = 0 (expansion RAM selected). But, if I'm reading figure 4-6 from the service manual correctly, /BANK3=0 AND /BANK6=0 will always be false because no two banks are ever selected at the same time. Decoders AA0037 and AA0038 are mutually exclusive, governed by the same logic: NOT (A15 AND (A14 OR A13)).
That is, it appears that for addresses 8000 to 9FFF, bank 3 is selected: /BANK3=0 and /BANK6=1. Or, am I missing something? —b9 On Wed, May 25, 2022 at 5:41 PM Stephen Adolph <twospru...@gmail.com> wrote: > 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 <hacke...@gmail.com> 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 <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? >>>>>>> >>>>>>> >>>>>>>
