VDP values for Screen Modes 0...8!

By Yukio

Paragon (1541)

Yukio's picture

29-10-2014, 20:53

Format:

SCREEN MODE

VDP MODE 0
VDP MODE 1
VDP MODE 2
VDP MODE 3
VDP MODE 4
VDP MODE 5
VDP MODE 6
VDP MODE 7

In decimal values:

Screen 0

0
112
0
128
1
54
7
241

Screen 1

0
96
6
128
0
54
7
1

Screen 2

2
96
6
255
3
54
7
1

Screen 3

0
104
2
128
0
54
7
1

Screen 4

4
96
6
255
3
63
7
1

Screen 5

6
96
31
128
0
239
15
1

Screen 6

8
96
31
128
0
239
15
1

Screen 7

10
96
31
128
0
247
30
1

Screen 8

14
96
31
128
0
247
30
1

In binary values:

Screen 0

0
1110000
0
10000000
1
110110
111
11110001

Screen 1

0
1100000
110
10000000
0
110110
111
1

Screen 2

10
1100000
110
11111111
11
110110
111
1

Screen 3

0
1100000
10
10000000
0
110110
111
1

Screen 4

100
1100000
110
11111111
11
111111
111
1

Screen 5

110
1100000
11111
10000000
0
11101111
1111
1

Screen 6

1000
1100000
11111
10000000
0
11101111
1111
1

Screen 7

1010
1100000
11111
10000000
0
11110111
11110
1

Screen 8

1110
1100000
11111
10000000
0
11110111
11110
0

Running Naked in a Field of Flowers

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By hit9918

Prophet (2866)

hit9918's picture

30-10-2014, 20:13

This reminded me of an issue I had with mode changes.
I had flipped mode registers to screen 0 (random in time) and for a frame openmsx showed it in an odd location.
Well but the real machine does the same.
I was surprised. My idea is that the VDP has everything as function of the scanline counter.
But screen 0 with its 40 chars, that number that is not 2^x, seems to have an extra address counter register.

This BASIC app shows the issue:

10 COLOR 15,4,5 : SCREEN 1 : SCREEN 0
15 PRINT:PRINT:PRINT:PRINT"text"
20 VDP(1)=96 : A=A/2/2
30 VDP(1)=112 : A=A/2/2
40 GOTO 20

randomly flippling the screen mode. the point being that the screen 1 letters stay solid in their location, while screen 0 jumps around.

The thing with scanline counter based addressing is that a when a line interrupt is late, there is only a local mess, maybe only one scanline.
while with address counters, the whole rest of the screen gets messed up, flashing with garbage.
Except screen 0, the VDP has the less fragile scanline counter based addressing.

By Latok

msx guru (3674)

Latok's picture

31-10-2014, 15:46

BASIC app? Are we going to call our listings 'apps' from now on? Hmpf...

By Grauw

Ascended (8405)

Grauw's picture

31-10-2014, 16:31

Funny, I kinda like it Smile. On PC / Mac desktop computers, the term program also slowly seems to be getting replaced with app after the term got popularised on the mobile platform…

By hit9918

Prophet (2866)

hit9918's picture

31-10-2014, 16:29

A test app for programmers to explore the platform Smile
And well it is such a nice short 3 letters word.

By Latok

msx guru (3674)

Latok's picture

31-10-2014, 17:47

Then name the BASIC program itself an app. But not the listing that generates the program.

By Manuel

Ascended (15697)

Manuel's picture

31-10-2014, 19:58

I remember using the word 'app' way before it become popular on mobile platforms. "Een appje" was Dutch for "a little program" (and now it seems to mean: a what's-app message...)

By Yukio

Paragon (1541)

Yukio's picture

31-10-2014, 20:23

Maybe ... And their could be related to "Mobile Phones" like the LGE ...
(LGE is the "Korean Factory")

Imagine something like a MSX-Player for Mobile Phones ...