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?
>>>>
>>>>
>>>>
