TMSS

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Okie
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TMSS

Post by Okie » Wed Jul 21, 2021 6:59 pm

Why is it necessary to write ‘SEGA’ to $100 when we will move.l #'SEGA'0x00A14000 if we determine the console is model 2 anyway? Just something that I don’t get. Also what is the difference that the version of the megadrive is HARDCODED into the I/O chip versus the other pins like LANG PAL DISK . How is it read without a pin. And are these pins what is properly known as System Bus lines?

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Re: TMSS

Post by Okie » Mon Jul 26, 2021 6:37 pm

Clarification on this would be appreciated . :D

TmEE co.(TM)
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Re: TMSS

Post by TmEE co.(TM) » Mon Jul 26, 2021 7:25 pm

Not doing the SEGA write results in VDP not cooperating with you on hardware that requires this write and that's what the version register will tell you if it is necessary to do so. The value is hardcoded in the ASIC and cannot be influenced by normal means, there's only 0000 and 0001 in all the existing hardware.
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Re: TMSS

Post by Okie » Wed Jul 28, 2021 5:12 pm

Thanks , so my question is why write sega to 0x00A14000 if we have it in the header vector region at 0x100? Are they distinct from each other.? I know much of the lower section of header vector is just meta data only the emulator will read.

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Re: TMSS

Post by TmEE co.(TM) » Wed Jul 28, 2021 5:18 pm

The SEGA write existed before TMSS ROM did, though it became actually functional with the introduction of TMSS with VA5/6 MD1 hardware. It was part of a copyright thing that all ROMs must have in them prior to introduction of the TMSS ROM which did its own verification on top while retaining the stuff that older things had to do anyway.
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Re: TMSS

Post by Okie » Wed Aug 11, 2021 4:14 pm

Thanks for replies , I am don’t understand what the difference from TMSS and Sega write . Is the difference that one writes to address 0x100 in header vector and the other is Write ‘Sega’ to $A14000. Referencing this patent, https://patentimages.storage.googleapis ... 796940.pdf. I am guessing figure 3 is the write of sega to $100 header vector and figure 4 is what is called the tmss write?
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Re: TMSS

Post by TmEE co.(TM) » Wed Aug 11, 2021 10:11 pm

TMSS ROM inside the MD (if present) checks for presence of "SEGA" or " SEGA" at $000100 in your ROM, if found it will boot your ROM. Otherwise it just enters an idle loop and the ROM will not be started and you won't get to see the "produced by...." screen. TMSS ROM has no relation to the $A14000 register and is a completely separate entity that 68K sees before it sees your ROM. Another register ($A14100) will choose if 68K sees the TMSS ROM or your cartridge ROM. You can see what TMSS does in here : http://www.tmeeco.eu/SMD/TMSSCODE.ASM

Once your ROM is booted, your code in the ROM then writes "SEGA" to the $A14000 register to make VDP function right, if the hardware requires it to do so.
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