Backup devices in SMS mode

For hardware talk only (please avoid ROM dumper stuff)
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KanedaFr
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Backup devices in SMS mode

Post by KanedaFr » Tue Feb 10, 2009 12:33 pm

While cleaning my website, I came back to the backup devices part...
I noticed the BIOS of the backup devices I knew are SMS code...
So it means they works in SMS mode...and so came the questions :)

- why SMS mode ? why not a plain genny code ?
- how did they reset the genny from software ? and reset from SMS to Genny mode !?

Notice I never looked at the SMS mode of the genny.

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Re: Backup devices in SMS mode

Post by Snake » Tue Feb 10, 2009 9:14 pm

KanedaFr wrote:- why SMS mode ? why not a plain genny code ?
Well it could be because they knew Z80/SMS better than they knew 68K/Genesis. But it's more likely because it was easier to work with their hardware in SMS mode.

The things all use 8 bit RAM. This is the reason for the slightly odd format that is .SMD. One bank of RAM (8KB) is banked in at a time and the .SMD data copied directly to it - later on, odd and even banks will appear on the Genesis side as high and low bytes of the 16 bit data bus. This is also the reason that earlier models of these devices maxed out at 16Mbit, since 8KB*256 banks == 16Mbit.
KanedaFr wrote:- how did they reset the genny from software ?
They didn't... It's all hardware.
KanedaFr wrote:and reset from SMS to Genny mode !?
The Genesis boots into SMS mode via a pin on the cart port. All they need to do is switch that pin and hit the reset line - voila - rebooted into Genesis mode.

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Post by KanedaFr » Wed Feb 11, 2009 11:06 am

:D I first thought the same (Z80 easier to code) but I thought I can't be the reason ;)

from what you said, it's so possible to make a interface in genny code to select a game or load a game from somewhere (floppy, usb, sd..) and ask for reset...and boot this game
I ask this because I never saw a multigame with a game selector (you needed to use reset button to select your game) while the 16in1 let you select your SMS game throught a menu. but perhaps it's only a money issue.

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Post by TmEE co.(TM) » Wed Feb 11, 2009 11:14 am

you only need to work out the HW in the cart... you have a lot of singals on MD cartslot :)
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Post by Shiru » Wed Feb 11, 2009 3:01 pm

KanedaFr wrote:I ask this because I never saw a multigame with a game selector (you needed to use reset button to select your game)
First time when I saw SMD, it was Genesis-like clone, and it had built-in (second slot inside the case, under the pcb) multi-game cartridge with menu, similar to NNN-in-1 for NES. Can't remember all the games, I'm sure there was Streets of Rage, Rambo III, probably Tetris, and large part of list was different levels of this games. Never seen anything similar after.

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