Yamaha CX5M, CX5M II, CX7M

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By zPasi

Champion (499)

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01-02-2016, 22:36

Alexey wrote:
zPasi wrote:

Very tempting. Well, seems my real CX5MII board is not the same as CX7, but the replacement YIS503II should be. How much RAM is in your board?

The RAM board can have either 512kb or 1024kb of RAM. Note that CX7 is not the machine name, it's the board type that was inside some of CX5MII (probably later versions). If you have a different motherboard with 2 connectors, then this RAM module will not fit there. On CX7 board it works out of the box. On the Russian MSX1 mainboard you will need to do some modifications (see below).

My real CX5MII board has 2 connectors for the RAM module. The KYBT1 YIS503II board I bought has one, and one for the VRAM. There is 'YIS 604, CX 7, CX 7M' printed on it.

Alexey wrote:

The VRAM expansion board should work out of the box with MSX2 ROMs, but you need to solder one wire to the drilled out VDP line on the back side of the board to get 128kb of VRAM

What wire is that? Maybe that's the reason my VRAM with SRAM test failed, I didn't have that wire.

By Wierzbowsky

Guardian (3430)

Wierzbowsky's picture

01-02-2016, 22:57

zPasi wrote:

What wire is that? Maybe that's the reason my VRAM with SRAM test failed, I didn't have that wire.

The VDP can address up to 192kb of VRAM. It has 3 CAS pins, each of those can control 64kb. On the board only one CAS goes to the VRAM connector. The second CAS line is cut by the drill at the factory. So if you want 128kb, you need to connect this disabled line to your VRAM board. However as you are using a single SRAM chip, I am not sure how this can be done. My board has 4 DRAM chips, 2 of them are using the CAS from the connector, the 2 others have to be connected with a wire to the drilled out CAS line.

By zPasi

Champion (499)

zPasi's picture

02-02-2016, 16:20

Alexey wrote:

However as you are using a single SRAM chip, I am not sure how this can be done. My board has 4 DRAM chips, 2 of them are using the CAS from the connector, the 2 others have to be connected with a wire to the drilled out CAS line.

My circuit is This one from the thread Is the V9938 compatible with SRAM ?. It only requires one CAS line. So there must be some other reason it doesn't work properly, but nevermind about that.

We may continue by mail about those boards.

By zPasi

Champion (499)

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08-02-2016, 22:19

Well, I didn't get that simple VRAM SRAM circuit working. When V9938 uses the memory, first it sets the row address bits, and lowers the RAS. Then it sets the column addr bits and lowers one of the CAS lines. When using RAS for CS and just one CAS only as an address bit, there is no way to detect precisely when the col addr bits are in place. So, I guess it is all about the timing, and even slight variations in the speed grade of the chips, make the difference if it works or not.

So, I'll do that in the old-fashoned way, with DRAM chips.

Then, it came to my mind if I should try to do MSX2+ conversion. I'd need a V9958, seems to be available on eBay. Then, a different BIOS. What else?

Speaking of BIOS, those roms Alexey linked, seem to be Russian versions. I don't have a Russian keyboard, and I don't need one, so I can't use these roms directly. But at least there is info of what parts are patched, for that missing RTC.

By Wierzbowsky

Guardian (3430)

Wierzbowsky's picture

08-02-2016, 22:32

The Russian BIOS has never harmed any humans. Smile Well, to my best knowledge of course... You are using English layout by default there anyway. I don't think there's a non-Russian BIOS for MSX1->MSX2 conversion that ignores RTC, so you will either have to adapt the original BIOS yourself, or you will have to use the provided one.

About MSX2+ conversion - I can provide you with MSX2+ BIOS and SubROM made for Yamaha YIS503III by Caro. But no one has ever tested it on a converted MSX1 board, so I presume you will need to make your MSX1 board fully MSX2 compatible before the MSX2+ conversion. If you would really like to make an MSX2+, it's easiler to get YIS503III and convert that one directly. There's a video how to do this on Youtube by our group member Dmitry Pugachev:

https://www.youtube.com/watch?v=dz-oaFYrFdg

By Piter Punk

Master (227)

Piter Punk's picture

09-02-2016, 05:46

Alexey wrote:

The Russian BIOS has never harmed any humans. Smile Well, to my best knowledge of course... You are using English layout by default there anyway. I don't think there's a non-Russian BIOS for MSX1->MSX2 conversion that ignores RTC, so you will either have to adapt the original BIOS yourself, or you will have to use the provided one.

Some Brazilian conversion kits had a patched ROM to ignore the RTC. You can find them at MSXPro. This other page at MSXPro is a tutorial about converting a 80 columns cartridge in a MSX2 upgrade kit. The Sub-ROM used in this kit ignore the RTC, too. But I guess the Sub-ROM isn't sooo different between these versions and the Russian mod, probably the changes are the same.

By l_oliveira

Hero (534)

l_oliveira's picture

09-02-2016, 20:06

You probably will find what you need here:

https://code.google.com/archive/p/msxnewbios/

That assembles fine with sjasm and you can customize what you want to build.

By zPasi

Champion (499)

zPasi's picture

09-02-2016, 22:11

Alexey wrote:

The Russian BIOS has never harmed any humans. Smile

It seems to make the international keyboard behave funny Smile
Like the matrix was different.

Yeah, I'll do the MSX2 mod first, MSX2+ maybe later (and on another machine, perhaps).

By zPasi

Champion (499)

zPasi's picture

09-02-2016, 22:17

l_oliveira wrote:

You probably will find what you need here:

https://code.google.com/archive/p/msxnewbios/

That assembles fine with sjasm and you can customize what you want to build.

Wow! I'll explore that later

By zPasi

Champion (499)

zPasi's picture

13-02-2016, 22:20

I managed to install that Alexeys VRAM board. Strange, but there seems not to be any connection to the V9938 CAS1, even when there is room for more VRAM. Well, i soldered that wire directly to the pin, then.

And something was still wrong. After hours of head-scratching, it finally came to me: the problem is not the VRAM at all, it must be the RAM mapper! The CX5MII BIOS initialises the mapper, but apparently this YIS503IIR was shipped without a mapper, and even without MAPWR and MAPRD lines. So it probably doesn't initialise any mapper.

I bet, when booting a cartridge game, not anything initialises the mapper. That's why even MSX1 game, like Nemesis 2, can fail. Aleste 2 (a disk game) probably handles the mapper itself so it works.

My mapper is CPLD based, so I can alter that to self-initialise. But haven't any more time for this right now, it will have to wait a few days...

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