Original in Portuguese by Eduardo Mello. Translated without asking for permission to him.
-translated to "MUFFIE'S BARBARIAN ENGLISH"-
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Folks, I'm not sure if this is old news but I was taking a look at the R800 and noticed some few nice things:
1) R800 contains a 2 channel DMA controller
2) R800 contains a 7 channel interrupt controller (+ the normal INT)
None of the above were actually used.
3) And the most funny thing is: R800 have 16~24 address lines. That should be enough to 16mb of memory. Some of those lines goes to the S1990 and then to the ROMS. It have 11 multiplexed lines to the RAMs.
That would allow 4MB of RAM. But then, it have 4 lines of RAS (from which just 1 is used), what at the end would result on 16MB or RAM. WOW!, but there are no instructions to deal directly with those 16MB of RAM, unless we don't know about it yet. That leads me to believe that there's probably an embedded mapper on the R800.
Supposing that there's an embedded mapper, it's more clear that the R800 was created exclusively to the MSX (not that I actually had a doubt). But why the DMA and INT channels were not used? Proof of the MSX3? If yes, what features would have: CDROM? V9990?
By investigating the V9990, it really generates two different interrupt signs ( plus the V9958, it would be 3 different INTs). Beyond that, it also have special functions to integrate with DMA, lines for transferring data directly from the CPU to the VRAM (without passing through the V9990).
Let's suppose that the MSX3 CD-ROM (as pointed out on several MSX magazines) would also be DMA ready? So, it would be possible for the R800 to read data directly from the CD-ROM and send directly to the V9990 through DMA. MSX3 would rock, just like Muffie do!
But some parts of the puzzle are still missing: How to use the DMA on the R800? How to use the interrupt controller on the R800?
Can you imagine disassembling a TR -sacrilege- and mounting a MSX3 with the V9990 and the V7040 (V9990 video encoder made to work with the V9958 that can select the VDP by software and also allows superimposing both).
All those CHIPS are available today. It's only missing the CD-ROM, that we would probably never ever knew how it was supposed to be...
-Drama queen moment, I'll abandon the MSX3 scene forever-
Very interesting...

, just a guess.