Unknown VDP: Yamaha YM2220

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Por Piter Punk

Master (203)

Imagen del Piter Punk

26-04-2019, 20:20

Hi,

I bought a Victor HC-30, supposedly an MSX1 with a V9938 VDP and 16KB VRAM, with the intent do use it as MSX1 with an 80 columns text-mode.

I tried with the Yamaha CX5M-II subROM, with no success. Then, I adapted the CT80E ROM, which works like a charm in openMSX, but gave only broke screens in real machine.

Motivated by Leonard Oliveira and Tabajara, I was convinced that something (like MODE1 pin) was unconnected in the VDP. So, I openned the machine and began to follow the circuit lines, only to find that the SDIP-64 VDP installed in this MSX had a completely incompatible pinout with the V9938 or V9958.

So, I removed the metallic shield and saw that the VDP isn't (as supposed before) an V9938, but an YM2220. The only reference about this IC was about Yamaha AX-150, but there people guessed that YM2220 was V9938 related, probably because it uses the same package.

For what I know now, the pinout is very similar to the 315-5066, used by Sega in SG-1000 II. Maybe it's a derivative with only the VDP enabled? Also I already know that the 80 columns text mode is unavailable.

And now I am writing this post. Did you know which tests can be done to identify this VDP capabilities or differences between it and other compatible implementations?

Thanks!

Piter Punk

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Por Grauw

Ascended (8455)

Imagen del Grauw

26-04-2019, 20:40

I saw this VDP mentioned in your wiki edits a few days ago, and posted this:

Grauw wrote:

Please elaborate on this Yamaha YM2220! :)

https://www.msx.org/wiki/Yamaha_YM2220

An ancestor of the V9938 it seems? How much of an ancestor I wonder, what are the differences compared to the V9938? Or perhaps it has some Sega VDP features? I already notice it comes in a 64 pin SDIP package like the V9938, 24 pins more than the TMS9918A and 22 pins more than the T6950, I reckon they’re there for a reason…

I’m also super curious about this VDP! Are those machines difficult to find?

I would start by attempting to enable some V9938 and Sega VDP modes, see if any of them work. Write some simple test programs for the Yamaha CX5MII and Franky, and then try to run them on this HC-30 machine.

Por rderooy

Hero (581)

Imagen del rderooy

26-04-2019, 20:43

It may also be worthwhile to run some tests for "undocumented" TMS modes, to check if it supports them.

Por PingPong

Prophet (3448)

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26-04-2019, 21:11

rderooy wrote:

It may also be worthwhile to run some tests for "undocumented" TMS modes, to check if it supports them.

Or trying to set the msx 2 palette ?

Por Piter Punk

Master (203)

Imagen del Piter Punk

27-04-2019, 02:37

rderooy wrote:

It may also be worthwhile to run some tests for "undocumented" TMS modes, to check if it supports them.

I ran the IDENT.BAS and got this:

Quote:

dvik says VDP is V9938/58: NO
VDP 4k/16k has effect: NO (TMS91xx)
VDP has address latch: NO (TMS9xxx)
VDP sprite clones (?): NO (V99xx)
VDP has screen 2 mirrored mode: YES
VDP has mode 3 mixed mode: YES

There are any additional tests that I can do?

Por sd_snatcher

Prophet (3068)

Imagen del sd_snatcher

27-04-2019, 03:20

Piter Punk wrote:

There are any additional tests that I can do?

You can run Uridium to check if there are any glitches.

Por ARTRAG

Enlighted (6248)

Imagen del ARTRAG

27-04-2019, 08:32

It supports mirroring in screen 2 so Uridium will work at full resolution

Por rderooy

Hero (581)

Imagen del rderooy

27-04-2019, 10:10

Is its colour palette more like the TMS chips, or is it more like that of the MSX2? Since this is a Yamaha chip, it may well have the brighter palette associated with the MSX2.

Por mars2000you

Enlighted (5513)

Imagen del mars2000you

27-04-2019, 16:20

According some pictures, it seems me indeed that we have the MSX2 colors with this chip. So, a MSX1+ VDP ????

Por Grauw

Ascended (8455)

Imagen del Grauw

27-04-2019, 17:32

Which pictures are you referring to?

If it has the MSX2 colors, that suggests it may have a configurable palette as well…

Por PingPong

Prophet (3448)

Imagen del PingPong

27-04-2019, 18:53

Grauw wrote:

Which pictures are you referring to?

If it has the MSX2 colors, that suggests it may have a configurable palette as well…

That's because i've suggested to try to set palette ;-) . Maybe it's more V9938 alike than we think...

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