Unknown VDP: Yamaha YM2220

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By pgimeno

Champion (288)

pgimeno's picture

06-04-2020, 04:27

Piter Punk wrote:
rderooy wrote:

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.

Using COLORBAR.BAS, I compared with the image from Casio PV-7 and the only difference that I could spot was in color 14, which in the Victor HC-30 looks very close to white. To do this test, I used the the same LCD television and the RCA video output on both machines.

I've taken shots of the Philips VG-8020/40 (TMS9129NL, obviously PAL), Philips NMS-8250 (V9938 in PAL mode) and Yamaha AX-150 (YM2220 PAL). Same TV set, same camera, all of them connected through composite video.

I've manipulated the images as follows: 1) imported as JPG into GIMP; 2) cropped; 3) selected a rectangle of a uniform colour below each of the numbers, and used Gaussian Blur with a value of 32 px; 4) saved to PNG.

Step 3 was done for two reasons: removing noise (since these are supposed to be flat) and making the images smaller.

Please don't inline these pictures.




Based on that, I'd say that the YM2220 palette looks a lot more like the V9938 palette than the TMS9129NL palette. Possible exceptions are colours 3, 6, 9, 11, 12, 14, but the differences are small. Even if not apparent in the picture, colour 11 in particular is a very pale yellow, not white.

By sdsnatcher73

Paragon (1862)

sdsnatcher73's picture

06-04-2020, 04:47

Nice comparison, thanks for that! It kind of makes sense that the two Yamaha chips are more similar, they probably used standard designs for their internal DAC and it is even possible the V9938 design was based on the YM2220.

By mars2000you

Enlighted (5890)

mars2000you's picture

06-04-2020, 08:23

It explains why I thought the VDP of this machine was a MSX2 VDP V9938 just by seeing some screenshots of the machine in action. It was indeed difficult to imagine that the machine was hiding an unknown VDP.

By sdsnatcher73

Paragon (1862)

sdsnatcher73's picture

19-02-2021, 19:09

I have a Victor HC-30 now as well, the RGB image is very good and very much like V9938. It is like a CX11 which is also an MSX1 but wit my V9938 (there are more Yamaha machines like that as we know). It has a stuck spacebar for now so I can’t dump the ROMs just yet...

By mohai

Paladin (919)

mohai's picture

08-05-2021, 16:23

I wonder if the not-connected pins are any use at all, as the Sega version, or they are useless in rhe MSX version ?
Did anybody tested them?

By bsittler

Master (228)

bsittler's picture

08-05-2021, 20:31

They are not connected internally I think, the AX150 PCB even uses those pins as random staging areas for simplifying layout of some of the other signal traces!

There is some discussion and a link to PCB photos in several posts on this page of the reverse-engineering thread: https://msx.org/forum/msx-talk/emulation/dumpingreverse-engi...

By gdx

Enlighted (4385)

gdx's picture

09-05-2021, 09:28

Your MSX must have a problem because if you use the RGB output the TMS9129NL's palette is not like this one but rather a palette close to that one:


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