Every 8 lines scrolled horizontally

For anything related to VDP (plane, color, sprite, tiles)

Moderators: BigEvilCorporation, Mask of Destiny

Post Reply
M-374 LX
Very interested
Posts: 60
Joined: Mon Aug 11, 2008 10:15 pm
Contact:

Every 8 lines scrolled horizontally

Post by M-374 LX » Mon Mar 24, 2014 1:50 pm

Why does the VDP scroll every 8 lines horizontally when I try to scroll only one?

r57shell
Very interested
Posts: 475
Joined: Sun Dec 23, 2012 1:30 pm
Location: Russia
Contact:

Post by r57shell » Mon Mar 24, 2014 3:55 pm

Wrong scroll settings.
There are three different types of scrolling:
1) Whole screen
2) Cells (by 8 lines at once)
3) Lines
Dig into VDP settings (registers).
Image

M-374 LX
Very interested
Posts: 60
Joined: Mon Aug 11, 2008 10:15 pm
Contact:

Post by M-374 LX » Mon Mar 24, 2014 4:19 pm

I have found the problem: register 0x0B was set to 1. Changing it to 3 solves the problem.

Nevertheless, according to Charles MacDonald's VDP document, it should work if the register is set to 1. So, this seems to be a mistake in that document.
Last edited by M-374 LX on Mon Mar 24, 2014 9:11 pm, edited 1 time in total.

Charles MacDonald
Very interested
Posts: 283
Joined: Sat Apr 21, 2007 1:14 am

Post by Charles MacDonald » Mon Mar 24, 2014 8:25 pm

M-374 LX wrote:I have found the problem: register 0x0B was set to 1. Changing it to 3 solves the problem.

Nevertheless, according to Charles MacDonald's VDP document, it should if the register is set to 1. So, this seems to be a mistake in that document.
There's two line scrolling modes, 1 and 3. Mode 1 re-uses the first 8 words of the scroll table and applies them to all display lines, mode 3 maps the scroll table words to display lines like normal.

Section 13 has a more in-depth description of how the scroll modes work, but you're right, I should have clarified how they differ in the register 0x0B description.

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests