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
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.
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.
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.
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.
