Screen 8 is offically screen9, what happend to 8?

Champion (351)

18-12-2022, 19:38

Ok, I was just browsing the manual of V9938 and was analysing mode register 0,1,8,9.
I came to the simple conclusion 1 screen mode is 'hidden/undocumented/cancelled'.
If you look at the graphical sites / mode bits M5 M4 and M3, ignoring M2, M1 from VDP1, so them on 0

Here it comes:
The graphical screens are quite simple to activate.
I am discarding the other options...
The values for M5 M4 M3, should be the value of screen number -2.

screeen -2 M5 M4 M3
screen 9 -> -2 > 7 > 1 1 1 (screen 8)
screen 8 -> -2 > 7 > 1 1 0 (only selectable by vdp0 and 1)
screen 7 -> -2 > 7 > 1 0 1 screen 7
screen 6 -> -2 > 7 > 1 0 0 screen 6
screen 5 -> -2 > 7 > 0 1 1 screen 5
screen 4 -> -2 > 7 > 0 1 0 screen 4

I have not checked sprite table of other tables/ color tables, but their should be an explanation.
When I have results I will share.

Does anyone tested the mode between 7 and '8'/9...

بواسطة Metalion

Paragon (1628)

18-12-2022, 20:15

Isn't that the Korean Hangul screen mode ?

بواسطة sdsnatcher73

Enlighted (4294)

18-12-2022, 20:32

No Korean SCREEN 9 in Hangul BASIC is actually using VDP SCREEN 5 or 6 depending on the machine in question.

بواسطة Accumulator

Champion (351)

18-12-2022, 20:55

That is what is generally taken for the truth. However in my logic, hypothetically if screen 9 is used by Kanji/Hangul text mode I would expect the following values for M5-M1 11101 (screen 8 + the M1 Text mode bit from VDP#1), or the M1 bit from VDP#1 set with one of the screen 6 or 7, but this will result in a lower screen number than bit set M5-M3, as a result Kanji/Hangul/Chinese/Korean of other Asian characters will have a lower screen value than 9.
That said, what is the logic to ignore original screen8. Or would it be M5-M1: 11001 this would than produce a graphic screen of value screen 7 + 1. But this one does not exist.
This is the real reason screen 9 is not there, because for some reason Yamaha skipped/neglected one screen mode and continued counting.

بواسطة NYYRIKKI

Enlighted (6092)

18-12-2022, 21:10

Maybe 256x212, 4-color mode was planned, but not implemented?

بواسطة erpirao

Paragon (1334)

18-12-2022, 22:23

or 64 color mode with palette ?
64 color +512 palette+sc5 sprites will be great!

بواسطة Metalion

Paragon (1628)

19-12-2022, 07:33

A more readable version of your chart:

		   M5 M4 M3
screen 4 | 4-2=2 |  0  1  0
screen 5 | 5-2=3 |  0  1  1
screen 6 | 6-2=4 |  1  0  0
screen 7 | 7-2=5 |  1  0  1
screen 8 | 8-2=6 |  1  1  0 (unknown mode)
screen 9 | 9-2=7 |  1  1  1 (real screen 8)

بواسطة PingPong

Enlighted (4155)

19-12-2022, 08:49

Metalion wrote:

A more readable version of your chart:

		   M5 M4 M3

screen 8 | 8-2=6 |  1  1  0 (unknown mode)

What the VDP do with this setting?

بواسطة gdx

Enlighted (6431)

19-12-2022, 09:03

Accumulator wrote:

sdsnatcher73 wrote:

No Korean SCREEN 9 in Hangul BASIC is actually using VDP SCREEN 5 or 6 depending on the machine in question.

That is what is generally taken for the truth.

SCREEN9 uses two different graphic modes. It is described in detail in the wiki.

بواسطة Accumulator

Champion (351)

19-12-2022, 13:04

Thanks for modifying the table for better viewing.
I also checked the VDP from Sega master system/Genesis (also M5-M1 bits), and there is a mode with 64 /128 colors with 256 x 192/212.
Maybe the real screen 8 has to be activated by using the 'M0' / unused bits in VDP reg 0/1

@gdx,. So bit related the used mode of screen8 is actually screen 9. Are you talking about missing 8 or actual 9.
It could be a mode exclusive for a console/game manufacturer. (As discussed in the past about Konami, could be Sega as well )
Programmatic keeping in mind screen -2 in assembly do not match basic screen.

بواسطة PingPong

Enlighted (4155)

19-12-2022, 12:58

PingPong wrote:

Metalion wrote:

A more readable version of your chart:

		   M5 M4 M3

screen 8 | 8-2=6 |  1  1  0 (unknown mode)

What the VDP do with this setting?

Anyone has a real hw to see what happens when one set the vdp in this mode ?