Dual V9958 board

Supporter (8)

09-02-2016, 10:40

Did you make any progress on this ??

opcode wrote:

Hi there,

I am trying to create a video board with two V9958 superimposed. From the V9938 Techinical Data Book it is hinted that it is possible, but no example is given, neither any further information provided. Does anyone know how to connect two V9958 to work in parallel? I am looking for the simpliest way to do that. I am sure a half dozen connections between both VDPs would do the trick....

I believe that the pins which would do the trick are: YS, HSYNC, CSYNC, DLCLK, XTAL, VRESET and HRESET.
Maybe:

CSYNC -> VRESET
HSYNC -> HRESET
DLCLK -> DLCLK

XTAL using the same clock generator

YS of the primary VDP controlling transparency.

Can someone confirm or correct me please.

Thanks...

By Xenophon

Supporter (11)

11-02-2016, 15:47

4 x V9958s used in Superimpose mode !

I spotted this on YOUTUBE some time back , but they don't seem to be too forthcoming with Schematics and stuff !

https://www.youtube.com/watch?v=sXU9d-UAJCU

I'm not sure if you can buy these ?? Does anyone have more information on this ?

By tvalenca

Paladin (747)

11-02-2016, 17:55

I used to support those kind of initiatives... but, look:

Why do you want 4xV9958, if we almost don't have software for one V9958 alone? There are VERY FEW software that uses V9958 features.

The more I studied to develop an enhanced dual-VDP solution, the less I wanted to finish it as a product that anyone could use. Not because the complexity but because very few coders will code for it, and I'm not a great coder myself. The only thing I see happening nowadays is an add-on for V9990 cartridges to superimpose its output on top of MSX internal VDP.

By madscient

Master (193)

13-02-2016, 08:02

Even if there is no software for now, someone can develop it whenever.
If you don't need new software, you shouldn't also new hardware.

BTW, I think V9990 is useless anymore.
There is more useful, cheaper, and famous VDP such as 315-5124.

By taupter

Supporter (1)

02-02-2023, 10:46

Xenophon wrote:

4 x V9958s used in Superimpose mode !

I spotted this on YOUTUBE some time back , but they don't seem to be too forthcoming with Schematics and stuff !

https://www.youtube.com/watch?v=sXU9d-UAJCU

I'm not sure if you can buy these ?? Does anyone have more information on this ?

I got some further information about it, albeit just some scattered bits.

The VDU demo was written in BASIC. Interpreted. The trick is all VDPs share the same ports, thus you can use ordinary BASIC commands to draw in any of the VDPs. The way he uses to select which VDP(s) he'll write to is another control port. This control port selects VDPs attributing an OR logic, where every 1 bit represents a processor he'll write to. If any of the bits 0 to 3 were set, the corresponding processor would be able to receive commands, allowing the program to issue arbitrary commands to any combination of VDPs at will (he could, as an example, set the system.via POKE to enable all four VDPs and change their modes together issuing a single SCREEN command). Reading of course can only be done from a single VDP, but I'm not aware if he uses another port to select or the bits 4 to 7 (as a nibble) to define which VDP he'll read from.

A further development of him was the VSU (2 V9958, 4 V9990 and 1 OPL4), but I'm not aware of the specifics of the implementation.