SVI-738 VRAM upgrade

By protek

Expert (126)

25-11-2021, 20:55

If I upgrade the VRAM to full 128 kB, should the 738 still boot and run with the original ROM?

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By Manuel

Ascended (19685)

25-11-2021, 21:26

What do you mean with 'full 128kB'? Do you implement an MSX Memory Mapper?

By djh1697

Paragon (1736)

25-11-2021, 22:14

Why upgrade to 128k VRAM and use the original ROM's? There will be no benefit?

By djh1697

Paragon (1736)

25-11-2021, 22:14

Why upgrade to 128k VRAM and use the original ROM's? There will be no benefit?

By protek

Expert (126)

26-11-2021, 06:10

Manuel wrote:

What do you mean with 'full 128kB'? Do you implement an MSX Memory Mapper?

4 x 4464. That’s 128 kB, right?

I’ll update the ROMs too eventually, but I’ve got the VRAM chips ready.

By sdsnatcher73

Enlighted (4307)

26-11-2021, 06:32

Yes of course it will still boot, it will only use 16kB of VRAM.

By foody

Champion (497)

07-12-2021, 21:31

Can someone upgrade their MSX 1 to become MSX 2? Is that possible and is it worth it?

By CASDuino

Champion (360)

07-12-2021, 21:51

foody wrote:

Can someone upgrade their MSX 1 to become MSX 2? Is that possible and is it worth it?

Some MSX can be upgraded to MSX2 Yamaha CX5M-II but most can't.

There are a few potential Cart based upgrades but nothing in production AFAIK.

By Grauw

Ascended (10821)

07-12-2021, 23:09

There is some information on the MSX Info Pages.

And also on the wiki it says:

wiki wrote:

Given that the VDP is a V9938 it's possible to upgrade the SVI-738 to MSX2 by replacing the ROM and VRAM. On early versions of the PCB there was also place for MSX2 compatible RTC, battery & other related chips, but these were removed from the last revisions.

But there’s a lot you’ll have to figure out. In principle upgrading the VRAM, replacing the BIOS ROM by an MSX2 one modified to work without clock chip (if absent), and adding the SUBROM should do the trick for the most part. However how to wire all this up electrically, I have no idea.

By gdx

Enlighted (6439)

08-12-2021, 15:07

For the VRAM it easy because you only need to replace the four TMS4416 by four TMS4464.
For the ROMs, it's a little more complicated due to the keyboard layout and the missing the Sub-ROM. You have to patch an MSX2 Main-ROM to replace the original. For the Sub-ROM, there are a RS-232C ROM that you can modify to add it in the page 0. You must replace it with a 32K ROM.

http://kilroy71.fastmail.fm/spectravideo-svi-738-msx2-mod.html

For RTC, this is not essential but you may be able to make a cartridge for it later, and even add a cartridge slot or expansion bus to it.

By lkpalwa

Expert (118)

10-12-2021, 15:37

RTC support to SVI738 without the missing chips (location does not exists in PCB)
see my site for more info: https://www.infodocmsx.com/docs-copy