Yamaha CX-11 upgrade to MSX2

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By Alexandre_Taito

Champion (322)

Alexandre_Taito's picture

21-07-2018, 05:40

Hi All!
I'm trying to upgrade a CX-11 to MSX2. I know it is hard without the service manual, but I'm trying.
In my head, the steps are:
- Upgrade VRAM to 128K (a pair of 4464 on top of the 4464 pair, pin 16 of the top memories connected to pin 60 of VDP, CAS1)
- MSX 2.0 MAIN ROM (without RTC and F4 register code) on place of MSX1 MAIN ROM
- MSX 2.0 SUB-ROM in slot, CE/OE connected to /SLTSEL

It **should** work. But it isn't.
Did I miss something?
Thanks!
Alexandre

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By MSX4ever

Master (169)

MSX4ever's picture

21-07-2018, 09:07

Memory ?
(Yamaha CX-11 has 32 Kb in slot 0)

Do you use this :
https://www.msx.org/wiki/Yamaha_URM-01

By Jipe

Paragon (1351)

Jipe's picture

21-07-2018, 09:10

outwardly is the same of cx5 mII
can you take a photo of main board

By Alexey

Guardian (1985)

Alexey's picture

21-07-2018, 16:42

The MSX2 must have 128kb or RAM. Your computer has 32kb only. And you can't easily change that because you only have four x416 RAM chips on board. To install 128kb you will need four x464 chips and a mapper circuit. The boards I've seen are not easily upgradable to MSX2. Better to have the CX7 board for that.

By Philip

Champion (368)

Philip's picture

21-07-2018, 17:51

Perhaps it will work if you remove the internal memory and use an external mapper?

By Manuel

Ascended (15190)

Manuel's picture

21-07-2018, 18:44

MSX2 does not require 128kB or even a mapper... So that cannot be the cause, but perhaps it depends on what BIOS is used. 64kB is minimum though.

By NYYRIKKI

Enlighted (5199)

NYYRIKKI's picture

21-07-2018, 21:35

I would say plug back the original ROM you had in there. If you don't have short circuits or something like that the computer should boot like normal MSX1 even with the extra stuff. When the computer is running, test that all of the VRAM is working ok and you can see the SUB-ROM in area #0000-#3FFF correctly. (Yes, some small test routine programming required)

If everything still looks fine, write the configuration of your machine to BlueMSX / openMSX and test if it boots (copy your machine configuration to new profile and do the same modifications to the config). If the problem is in the ROMs, it should be much more easy to figure out what is wrong on the emulator environment.

By Alexey

Guardian (1985)

Alexey's picture

21-07-2018, 22:42

Ah, true, some MSX2+ had only 64kb and no mapper. But with 128kb having the mapper is a must. So it's possible to replace four x416 with two x464 to have the working MSX2 machine. But DOS2 will not load without an external RAM cartridge.

By Manuel

Ascended (15190)

Manuel's picture

21-07-2018, 22:46

No, all MSX2+ machines have at least 64kB RAM with mapper. But for MSX2 a mapper is not mandatory, so you can have 64kB without mapper.

By NYYRIKKI

Enlighted (5199)

NYYRIKKI's picture

21-07-2018, 23:21

Guys...
- Yes 32K RAM especially in slot 0 sounds really bad
- Yes 32K of RAM is under minimum specs of MSX2 standard
- Yes lack of minimum of 128K memory mapper prevents running of DOS2
- Yes you can't run even DOS1 without 64K of RAM.

How ever none of these explain why the computer does not boot! With the configuration Taito has he should be fine running almost every MSX2 BASIC program without problems. For any serious use this is too limited setup, but let's try to solve this problem first.

By Manuel

Ascended (15190)

Manuel's picture

21-07-2018, 23:57

Try such a config in an emulator... does it boot?

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