Wiki editing discussion | MSX Resource Center (Page 186/198)

Par mars2000you

Enlighted (6575)

07-04-2023, 18:09

Accumulator wrote:

What is the AT 990 chip exactly? could not find any documentation (AX-660 & AX-990)

As we know that the VRAM and the VDP are also used by the Sega part, maybe it's an Engine that controls the use of VDP and VRAM by the MSX1 or Sega part.

Par Accumulator

Champion (351)

07-04-2023, 20:52

I also think it is somekind of 'MSX-Engine', addressing the V9958., sound etc... I could not really find another controller on the board

Par Pentarou

Hero (568)

08-04-2023, 00:11

mars2000you][quote=Accumulator wrote:

As we know that the VRAM and the VDP are also used by the Sega part, maybe it's an Engine that controls the use of VDP and VRAM by the MSX1 or Sega part.

How do you "know" that?
The MD PCB on that photos is fully populated with the RAM for the 68k, the Z80 and the VDP.
Besides, it would be quite an achievement to use DRAM on the MD, since there's no refresh circuitry and the MD VDP uses dual ported VRAM.

Par gdx

Enlighted (6449)

08-04-2023, 01:59

Each PCB use its own RAM. Mega Drive PCB has 3 x 32kB (CXK58257M-85L or equivalent).
One is close to the Z80 and the other two are close to the 68000.

Par mars2000you

Enlighted (6575)

08-04-2023, 06:22

@gdx: for info about UM6561BF, look here: https://forums.nesdev.org/viewtopic.php?t=15342 - I guess the "B" maybe corresponds to a revision.

Interesting this precision:

Suffix info :
UM6561F-1 - NTSC
UM6561F-2 - PAL-B
UM6561F-3 - PAL-M
UM6561F-4 - PAL-N

Par mars2000you

Enlighted (6575)

08-04-2023, 13:12

@gdx: concerning AX-990 and its hidden 3rd slot, the info you have removed was correct - see the mentioned video at 4:57, which shows a 'multi-games' cartridge inserted there without its case.

Par mars2000you

Enlighted (6575)

09-04-2023, 17:19

Is the 3rd slot of AX-990 used in a similar way to this PCB: https://www.gadunky.com/product/megadrive-genesis_cartridge_... ?

The description precises that "This is a printed circuit board (PCB) for non battery save Sega Mega Drive/Genesis games. If your game has a broken board, or you want to play a ROM hack on actual hardware, this is for you."

Par gdx

Enlighted (6449)

10-04-2023, 11:53

The 3rd port is to put the PCB of a cartridge containing one or several games (or a flash card interface) inside in order to put these favorite games internally. As the Genesis normally only has one slot so it is the same slot in parallel and in this case we can't insert a cartridge at the same time in the external slot or else they have added a system so that the slot external takes priority. Indeed exact operation needs to be confirmed.

Par sdsnatcher73

Enlighted (4322)

13-04-2023, 13:47

Tested ML-30FD with 2 drives (set to DS2 and DS3) on ML-G30. The drives are not recognised so there is no support in the ROM for 4 drives. The manual mentions support for 5" (a common way to describe what we know as 5.25") drives. The only way they would work is if the internal drives are disconnected. Formatting will probably only be possible on 80 track so called 4DD drives, but reading disks should work (I will try if I can find some external drive unit probably for Fujitsu FM-7 as they use the standard Shugart connector).

Par Accumulator

Champion (351)

13-04-2023, 23:18

If you look close to the images in the wiki of AX-990, the 'SEGA' boards are completely different.
It seems there are different versions. Looks like one SEGA board is more relying on the MSX board, and other more independent.

On one image, the empty spot for an IC, is the 68000 missing.

I assume they are produced by Novatek Microelectronics in Taiwan. On the ic it is stated NT part No.

Maybe they are like the company Quanta, producing computers etc, on OEM base for almost any manufacturer