VRAM board for Yamaha CX5MII

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By Grauw

Ascended (8507)

Grauw's picture

29-06-2015, 21:14

More CX5MII guts pics:

Back of the board
Back of the vram module
1024k ram expansion module :)
VDP area close-up, top
VDP area close-up, bottom
Zip of all my CX5MII guts pics

As you may notice, the CAS1 line is cut (drilled). Originally it led to the VRAM expansion board connector, but it is replaced by the airwire from CAS0. So, the service manual is incorrect for the CX5MII.

By Alexey

Guardian (2434)

Alexey's picture

29-06-2015, 21:14

Pics can't be seen, browser says "forbidden".

So was CAS0 or CAS1 originally connected to the expansion board? Because this matters for the text I will put for the airwire connector. Is there a way to easily connect a wire to CAS pins of the VDP?

By Grauw

Ascended (8507)

Grauw's picture

29-06-2015, 21:42

Pics fixed. Wrong permissions for some reason. They’re quite high-res so you can zoom in a lot.

Looks like CAS1 was originally connected to the expansion board, for the CX7M probably. But in the CX5MII this line is cut and it receives CAS0 via the airwire in stead. The new CAS1 wire needs to be soldered directly on the VDP’s pin.

By Alexey

Guardian (2434)

Alexey's picture

29-06-2015, 23:16

Ok, here's the board with 4 4464 chips (128kb) and a pad to solder the airwire to CAS 0/1 of the VDP. If the board's CAS connector is routed to VDP's CAS0, then the airwire must be connected to CAS1 and vice versa.

I am not going to produce these boards myself unless I have at least 5 orders. Otherwise I can't even cover the expenses of making those boards. I am going to order my other boards soon, so if you need this VRAM board for your CX5MII MSX, please contact me ASAP.

If you want to produce these boards yourself, I can share the schematics and Gerber files. The only thing I will ask in return is 1 of these boards. I think it's fair enough.

By Grauw

Ascended (8507)

Grauw's picture

29-06-2015, 23:38

Nice! One order for me! Board + components if possible, I can assemble it myself Smile.

p.s. It will also work on the YIS503IIR, right? I’m sure some Russian MSX users will be interested?

By sd_snatcher

Prophet (3089)

sd_snatcher's picture

29-06-2015, 23:25

Humm, originally the board was indeed designed to have the 1st bank of 64KB onboard and the 2nd bank 64KB on the expansion.

In the wild you probably will find both possibilities: boards with CAS1 and others modded in-factory to have CAS0 on the VRAM expansion connector.

AFAIK, that won't change your expansion board design. The only difference will be that, when installing the board, the owner will have to connect the wire to the unused CAS accordingly.

By Alexey

Guardian (2434)

Alexey's picture

29-06-2015, 23:54

What I really wonder is how BIOS will know that there's enough VRAM to enable higher screens. I am afraid a patch for BIOS will be needed. Otherwise all this is in vain...

By Grauw

Ascended (8507)

Grauw's picture

30-06-2015, 00:02

That’s the next step Smile. As I mentioned earlier, the BIOS ROMs are socketed, one of which is a “sub-rom” (contains mode 80 support), so I hope it’ll be easy to modify.

But for now, some (European) software will probably bypass the BIOS and already work, and I can also try it out with my personal projects.

By gdx

Prophet (3076)

gdx's picture

30-06-2015, 08:07

Why not a PCB with 192 kB?

By Alexey

Guardian (2434)

Alexey's picture

30-06-2015, 08:08

Yes, I checked the pics of YIS503II board and it indeed is very similar to CX5MII. So I am pretty sure the board will work there. Thanks for the hint!

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