Yes, that helps quite a bit. Thank you. One more question: If you are already handling situations 1 & 3 — bank3 is low and bank 6 is high for both, so A15 must be checked — why not reduce the scenarios to a single rule:
- If either bank3 or bank6 is low, address is 0 to FFFF, rexcpm responds. —b9 P.S. Where can I read more about the data latched in by ALE? The Tandy 200 service manual and technical reference make it look like the AD bus is holding only the lowest 8 bits of the memory address, A7 to A0, so I do not yet understand how it contains A15. On Wed, May 25, 2022 at 6:10 PM Stephen Adolph <twospru...@gmail.com> wrote: > when bank3 is low, address 0000 to 7fff, bank6 is high, rexcpm responds. > > When bank6 is low, address a000 to ffff, bank3 is high, rexcpm responds > > When bank3 is low, address 8000 to 9fff, bank6 is high, rexcpm responds. > > All of these scenarios are unique. Cpm gets 64k when option rom and > optikn ram 2 are engaged. > > Yah? Hope that helps. > > Steve > > > > > On Wednesday, May 25, 2022, B 9 <hacke...@gmail.com> wrote: > >> 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? >>>>>>>>> >>>>>>>>> >>>>>>>>>
