Things I noted about R800 [Translation from MSXBR-L]

Door muffie

Paladin (933)

afbeelding van muffie

14-08-2009, 15:46

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...

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Van PingPong

Prophet (4093)

afbeelding van PingPong

14-08-2009, 16:57

Effectively, unlike the predecessors, v9990 was designed to allow direct VRAM memory access from a device... check the docs.

Van Leo

Paragon (1236)

afbeelding van Leo

14-08-2009, 19:32

few month ago i found that the kawasaki KL5C80 was quite close to r800, the instructions take the same cycles and but it has 512kb adress space and no dma only uarts

datasheet can be found here :
http://www.digchip.com/datasheets/download_datasheet.php?id=477383&part-number=KL5C80A12

by the way the s1990 was supposed to have some hidden register ( i read somewhere ) , maybe to interface with v9978

Van PingPong

Prophet (4093)

afbeelding van PingPong

14-08-2009, 22:04


by the way the s1990 was supposed to have some hidden register ( i read somewhere ) , maybe to interface with v9978

@leo:but the v9978 never existed, was a legend, or no?

Van Sonic_aka_T

Enlighted (4130)

afbeelding van Sonic_aka_T

14-08-2009, 22:44

AFAIK The V9978 was rebranded as the V9990. The PDF below would support this idea, but there is of course no way to check if that PDF is authentic or not. Well, not that there's really any reason to doubt it's authenticity...

http://www.datasheetarchive.com/pdf-datasheets/Datasheets-8/DSA-153438.pdf

Van Leo

Paragon (1236)

afbeelding van Leo

15-08-2009, 07:23

i know i know v9978 never existed and has been rebranded v9990 , i was talking about that possible msx3 that would have been r800 + S1990 + lets say better VDP with dma between ram and vram.
ANd what i am saying is that if we can find the meaning of these undocumented registers ( if they exist ) of the S1990 then we can have one more clue on what was supposed to be msx3 ( or fsA1XT )

Van NYYRIKKI

Enlighted (6016)

afbeelding van NYYRIKKI

15-08-2009, 11:55

Hmm... I can't help thinking that would it be possible to attach KL5C80 to MSX? I think it would give quite a nice speed boost compared to regular 7MHz upgrades... Big smile

Van Leo

Paragon (1236)

afbeelding van Leo

16-08-2009, 15:29

that kl5C has also the advantage to be the only 5V compatible z80 : ez80 is 3v3.

Van Leo

Paragon (1236)

afbeelding van Leo

10-03-2010, 16:53

Thinking in Z80 turbo kit upgrades , i have just noticed that Z280 is able to work at double internal speed wrt to external bus speed, thanks to the cache it has inside there is not a lot of speed lost , it is also fully pipelined so it can reach 1 instruction per cycle at 12MHz while working externally at
6MHz.
On top of that it is binary compatible with R800 , it is not surprising since Z280 is the CMOS version of the Z800 in NMOS that never got produced, and that R800 has taken some parts of the Z800...

An other similarity between R800 and Z280 , they are the only Z80 cores that manage 16MB with MMU,the Z180 stops at 1MB : that makes me think that the datasheet of the Z280 could be used for enabling MMU and DMA use on R800 Hannibal , just a guess.
Z280 can be easily bought at utsource.net (i did it) ... as well as V9990 ... as well as V9958 ...
cheers,