Alternative SVI-728 color pallette?

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By Manuel

Ascended (15839)

Manuel's picture

31-03-2018, 18:02

The wiki article on this machine says

Quote:

You could select alternative color palette with command VDP(0)=VDP(0)OR1

How does this work? It has a simple TMS9xxx VDP right?

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By mars2000you

Enlighted (5515)

mars2000you's picture

31-03-2018, 18:18

I guess the difference is in the BIOS. This feature has been removed on the SVI-738, which has the MSX2 VDP.

Here's the comparison between SVI-728 and SVI-738

Rechercher différences

1. C:\blueMSX 2\Machines\MSX - Spectravideo SVI-728\728bios.rom: 32.768 octets
2. C:\blueMSX 2\Machines\MSX - Spectravideo SVI-738\738bios.rom: 32.768 octets
Offsets: hexadéc.

   2:	D7	5C
   3:	02	01
  2B:	11	91
 15C:	00	3E
 15D:	00	02
 15E:	00	D3
 15F:	00	99
 160:	00	3E
 161:	00	89
 162:	00	D3
 163:	00	99
 164:	00	C3
 165:	00	D7
 166:	00	02
1012:	20	1F
1014:	9E	9D
101B:	20	1F
1023:	97	96
104F:	00	30
1050:	00	31
1051:	00	32
1052:	00	33
1053:	00	34
1054:	00	35
1055:	00	36
1056:	00	37
1057:	00	38
1058:	00	39
1059:	00	2C
105A:	00	2E
107F:	81	83
1080:	82	88
1081:	84	8C
1082:	86	93
1083:	87	96
1084:	91	84
1085:	94	89
1086:	A4	8B
1087:	B1	94
1088:	B3	81
1089:	B5	98
108A:	B7	A0
108B:	B9	82
108C:	83	A1
108D:	85	A2
108E:	88	A3
108F:	89	85
1091:	8B	8D
1092:	8C	95
1093:	8D	97
1094:	93	B1
1095:	95	B3
1096:	96	B5
1097:	97	B7
1098:	98	A4
1099:	A0	86
109A:	A1	87
109B:	A2	91
109C:	A3	B9
109D:	65	79
109E:	79	41
109F:	9A	45
10A0:	90	49
10A1:	8E	4F
10A2:	8F	55
10A3:	80	8E
10A4:	92	45
10A5:	99	49
10A6:	A5	99
10A7:	B0	9A
10A8:	B2	59
10A9:	B4	41
10AA:	B6	90
10AB:	B8	49
10AC:	41	4F
10AD:	41	55
10AE:	45	41
10B0:	45	49
10B1:	49	4F
10B2:	49	55
10B3:	49	B0
10B4:	4F	B2
10B5:	4F	B4
10B6:	55	B6
10B7:	55	A5
10B8:	59	8F
10B9:	41	80
10BA:	49	92
10BB:	4F	B8
10BC:	55	59
10BD:	45	00
10BE:	59	00
1B94:	C3	18
1B95:	AC	16
1B96:	1B	30
1B97:	30	83
1B98:	83	33
1B99:	33	10
1B9A:	10	34
1B9B:	34	36
1B9C:	36	35
1B9D:	35	10
1B9E:	10	3A
1B9F:	3A	C3
1BA0:	C3	3C
1BA1:	3C	10
1BA2:	10	3D
1BA3:	3D	46
1BA4:	46	41
1BA5:	41	10
1BA6:	10	42
1BA7:	42	06
1BA8:	06	FF
1BA9:	FF	10
1BAA:	10	00
7754:	40	00
7757:	14	12
7F55:	27	25

118 différence(s) trouvé. 

By mtn

Master (248)

mtn's picture

31-03-2018, 19:12

Yes, I remember playing around with this on my SVI-728 back in the 80's. If I remember correctly, the "new" color-set gathered were mostly brownish, although I had a crappy CRT television at the time.

It would be interesting to know what the thought behind this was, my first idea now is perhaps it were colors that facilitated sharpness using the Spectravideo 80-columns adapter?

Im only beer-guessing though..

EDIT:

Hm, wasnt that 80 col adapter monochrome?

(Not much use for beer guessing.)

By Manuel

Ascended (15839)

Manuel's picture

31-03-2018, 21:11

My point is that the MSX1 VDP does not have an adjustable palette. So, I wonder how it works, hardware wise.

By sd_snatcher

Prophet (3093)

sd_snatcher's picture

31-03-2018, 21:40

The TMS9918 datasheet states that:

Quote:

Enabling the bit EV in the TMS9928A/9929A causes A-Y and B-Y to go to the sync level only when all planes in front of the pixel under question are transparent.

Depending on the TV-Encoder chip being used, this will make the color-burst go out of sync, and the colors will be affected on the CVBS output. They shouldn't be affected in the RGB output though.

It's not an alternate palette. It's just a side effect because there's no external VDP present. And the effect will vary from machine to machine and from TV to TV. Not reliable for any usable application.

By Manuel

Ascended (15839)

Manuel's picture

31-03-2018, 22:27

So where did that information in the Wiki article about the 'colour palette' come from? I guess it was "common knowledge" found out by users, but not something official (from a manual for instance), am I right?

By NYYRIKKI

Enlighted (5402)

NYYRIKKI's picture

01-04-2018, 04:58

Manuel wrote:

So where did that information in the Wiki article about the 'colour palette' come from? I guess it was "common knowledge" found out by users, but not something official (from a manual for instance), am I right?

Correct... SVI-728 had no RGB-output, so I doubt that anyone has really tested that scenario in real life, but it is easy to believe that sd_snatcher is correct here. (Thanks for explaining) The palette that I added to the wiki was translated from local magazine I stumbled in to. I remember that I tested this ~30 years ago and the effect was pretty much as described in the magazine. I remember that playing ie. BMX simulator was much better looking with brown color. Smile

By Manuel

Ascended (15839)

Manuel's picture

01-04-2018, 08:31

Anyway, so the effect will be like that on any MSX with a similar CVBS output circuit, right?

By eimaster

Master (222)

eimaster's picture

14-04-2018, 22:46

Does openMSX show this effect when emulating SVI-728 and entering VDP(0)=VDP(0)OR1 or no?!

By Manuel

Ascended (15839)

Manuel's picture

14-04-2018, 22:50

No.

By sd_snatcher

Prophet (3093)

sd_snatcher's picture

15-04-2018, 05:24

Manuel wrote:

Anyway, so the effect will be like that on any MSX with a similar CVBS output circuit, right?

If "similar CVBS output circuit" means:

- The same TV-Encoder
- The same TV color system (PAL)
- Same TV set

Then the answer might be "yes".

But even if the TV set changes, the results might differ.

Just out of curiosity, I tested it in my Sharp Hotbit 1.2. The result was that the TV stopped recognizing the color carrier at all, and the image just displayed as black & white.

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