NMS8245 2+ upgrade

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By Philip

Champion (363)

Philip's picture

10-08-2018, 22:48

So I just finished my 2nd msx2+ upgrade. This time a nms8245.
Since it was kinda hard to find these instructions, I will just dump them here Smile

Installing the v9958
Cut out the v9938, remove the remaining pins and solder.
Solder a socket in place of the v9938

On the v9958 these pins have to be bend so they are not inserted into the socket:
4 (vreset) (Should not be needed as it does not seems to be connected in nms8245...)
26 (wait)
27 (hreset)
21 (vdd)

Then connect these pins together on the v9958:
1, 4 and 27
21 and 58

Installing the ROM
Since there is no F4 port, make sure the F4 port stuff is disabled in the BIOS.
Create a 27c512 or similar system rom with this layout:
0000-7fff basic-bios
8000-bfff subrom
c000-ffff diskrom

For the kanji rom I've used a 27c512 but a 27c256 should also work.
It should have this layout (for a 27c256 just skip the 2nd half):
0000-3fff kanji rom 2nd 16k block
4000-7fff kanji rom 1st 16k block
8000-bfff kanji rom 2nd 16k block
c000-ffff kanji rom 1st 16k block

Insert the system rom in the rom socket.
Bend pin 27, 20 and 22 on the kanji rom and install it on top of the system rom.

Connect the bend pins as following:
- pin 27 on A14 i.e. pin 25 cardridge slot
- pin 20 on CS12 i.e. pin 3 cardridge slot
- pin 22 on slt3/30 i.e. pin 48 of the gate array. There is a nice place to solder it right above pin 48.

That's it!

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By Angelo Sanna

Supporter (14)

Angelo Sanna's picture

11-08-2018, 00:20

Hi Philip, you can find schematics on the website from Hans Oranje for the F4 adress decoder and latch in a 8245. It looks like this:

By Pablibiris

Paragon (1677)

Pablibiris's picture

11-08-2018, 10:18

Great work Philip!!

By hamlet

Scribe (1736)

hamlet's picture

11-08-2018, 13:50

Hooray Philip!

By pix retro

Rookie (20)

pix retro's picture

21-08-2018, 00:49

Is this an upgrade to 2+? Ooooooh

By karloch

Paragon (2017)

karloch's picture

21-08-2018, 18:03

Very valuable, thanks for sharing! By the way, after ROM upgrade the boot up logo is lost right? Why is that? I never understood quite well the dependencies for MSX 2+ boot up logo display.

By msd

Paragon (1359)

msd's picture

21-08-2018, 20:27

It is related to the f4 register. It stores hard or soft reset. at reboot it checks state in the f4 register ; but if not implemented you Will either never get the boot logo or always . Probably never

By luppie

Paladin (842)

luppie's picture

21-08-2018, 20:30

karloch wrote:

Very valuable, thanks for sharing! By the way, after ROM upgrade the boot up logo is lost right? Why is that? I never understood quite well the dependencies for MSX 2+ boot up logo display.

The F4 adress decoder and latch are needed for the boot logo

Edit: msd also pointed this out Big smile

By Philip

Champion (363)

Philip's picture

21-08-2018, 21:01

Another reason the boot logo is lost, is that it is in the kanji Rom. Which doesn't fit into the 64k Rom of the 8245.
That's why in the instructions there is another eeprom with the kanji Rom installed on top of the normal eeprom.

The bios can be patched to not look at the f4 register and always show the boot logo.
The only problem is that the memory counter overwrites memory and thus some software which reboots the computer to initialize itself won't work.
However these programs are quite rare.

By karloch

Paragon (2017)

karloch's picture

21-08-2018, 23:12

Thanks for explaining it! Maybe I would remain with 2.1 ROM just to keep the logo Smile

By msd

Paragon (1359)

msd's picture

22-08-2018, 11:56

Another reason the boot logo is lost, is that it is in the kanji Rom. Which doesn't fit into the 64k Rom of the 8245.
I doubt that. The kanji is in a different rom iirc, when msx2 are modified to 2+ this is not included anyway, but perhaps an already modified ROM was just for this. I have a nms8245 modified to 2+ which has a boot logo.. (it ofcourse has the f4 register).

Best is to add this register.. keeping the 2.1 rom is just not as good as it can be imho.

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