About MSX2+ upgrades...

By gdx

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11-05-2021, 10:17

I planed to upgrade my FS-A1 to MSX2+.

I thought I can also replace the main ROM and the sub ROM easly by using Roms from FS-A1FX. I thought the only obstacle was port # F4 but that's far from being the case.

Japanese MSX2+ have among others a Kanji driver in its Sub-ROM. MSX2+ Sub-ROM size is 48kB not 16kB as the MSX2s! These are not two separate things as it is often said. The MSX logo routine is in the aera 7A00h-7FFFh.

So adding #F4 port and/or patching the Main-ROM is insufficient to upgrade an MSX2 to MSX2+. We have to replace the Sub-ROM too. FS-A1 requires also adding the memory mapper (that is standard in MSX2+) and Kanji-ROM (otherwise the kanji doesn't make sense), and non Japanese MSX2+ doesn't exist so we do not have an sample to create one ROM set.

So I think just replacing the V9938 by V9958 is relevant. It requires slight modification and it makes work many MSX2+ games.

I do not recommend using the available patched ROMs, all those I have found are poorly patched. Do it only if you master really the subject.

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By gdx

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11-05-2021, 13:17

I made a Rom set for the FS-A1.

MSX2+ logo is displayed on emulator even if you choice a version without port #F4 support but I not sure If it's the case on an Real FS-A1.

Does anyone have an FS-A1 with a V9958 to try it?

There are also Japanese characters to test to see if they match the keys. If these two things work, the majority of MSX2+ games should work except Kanjis.

By gdx

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12-05-2021, 12:38

Here are some explanations because yesterday I did not have time.

The FS-A1 has its system and firmware bundled into a 128kB ROM. To do the MSX2+ upgrade, I used the FS-A1FX ROMs.

- The first 32kB contain the Main-ROM that is placed in slot 0 at address 00000h.
- The next 16kB contains the Sub-ROM followed by 16kB filled with FFh. The Sub-ROM is placed in slot 3-1 at address 00000h.
- The following 32kB contain the first part of the firmware that is placed in slot 3-2 at the address 04000h.
- The last 32kB contain the second part of the firmware that is placed in slot 3-3 at the address 04000h.

The first problem is how to separate the Sub-ROM from the Kanji-Driver to reduce the size. Already I know that the routine to display the logo is in the Kanji-Driver part at the address 07A00h until 07FFFh (MSX address). So for it to be displayed, you must check that the 16kB part filled with FFh is placed in slot 3-1 at the address 04000h. I have forced hard-reset mode in "NoF4" ROMs so if the 16kB part behind the Sub-ROM is placed behind the Sub-ROM in the same slot, the logo will be displayed by adding the routine. Otherwise, you must force the soft-reset mode.
If there is no other routine from the Sub-ROM in the Kanji-Driver part. The MSX2+ update can be completed by adding a cartridge containing a Kanji-Driver and a Kanji-ROM. Without it, Kanji-BASIC works but only ANK characters will be displayed, However the software will work

The second problem is the keyboard which is not the same. For example, Kanas are arranged differently on the keyboard. I patched the Main-ROM to fix it but that should be checked on a real FS-A1.

The third problem is RAM. Although the S1985 can support a memory mapper up to 512kB. This is not used for internal 64kB. It is therefore necessary to make the following update or to use a cartridge.


Once these 3 three problems are overcome, there are some details to settle according to your tastes. I made different versions of ROM including one with the original firmware (that is useless but there are people who prefer to keep it). You can patch this ROM to prevent it from starting by default.


I also made 66kB ROMs without firmware, with the system only because I don't know which ROM to use to replace the original 128kB. I also made a ROMs with the X-BASIC v2.1 (BASIC-Kun) instead of the firmware. It is possible to add a 32kB ROM (slot 3-3) to it if you want.

By gdx

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19-05-2021, 15:46

I replaced:




I added the laster kanji driver. It supports MSX-JE except that of the Japanese MSX-Write I because this one is bugged when used on MSX2+.

Download: ROM_For_FS-A1_Upgraded_To_MSX2plus.zip