VDP 32X Modes

Ask anything your want about the 32X Mushroom programming.

Moderator: BigEvilCorporation

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

VDP 32X Modes

Post by r57shell » Mon Oct 14, 2013 9:57 pm

I don't have 32X, but I'm updating gens rerecording emulator.
So, I have some questions:
1) Does Mode 0 (32X off) support all mode of Genesis, like interlaced and so on...

2) Does Mode 3 (Run length mode) support priorities.
I mean:
a) pixel priority = (color priority) XOR (PRI register)
b) pixel overlaps if it's priority = 1 otherwise it is backdrop.

3) Is it possible to change Mode for rows independently during HBLANK?

If there are some docs, with answers, I would like to get link.

Thanks
Image

ob1
Very interested
Posts: 403
Joined: Wed Dec 06, 2006 9:01 am
Location: Aix-en-Provence, France

Post by ob1 » Sat Jun 21, 2014 4:40 pm

Hello r57shell.
I have never tried your questions, but here are my answers, much helped by the "32x docs" topics and the 32x hardware manual especially
  • Yes, with 32x mode 0 (blank mode), you can have any Genesis video mode (32x Hardware Manual, §Display mode)
    I can't see why, in mode 3, you wouldn't have priorities (32x hardware manual, §Priorities)
    Yes, and much to my surprise, you can change the mode any time you like, noting : "Switching is always allowed, but is valid from the next line" (32X hardware manual, VDP registers - Display mode selection)

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

Post by r57shell » Sat Jun 28, 2014 12:35 am

ob1 wrote:Yes, with 32x mode 0 (blank mode), you can have any Genesis video mode (32x Hardware Manual, §Display mode)
Somewhere I saw words that 32x working only in one display mode.

ob1 wrote:I can't see why, in mode 3, you wouldn't have priorities (32x hardware manual, §Priorities)
I don't remember anymore why I was asking this.

ob1 wrote:Yes, and much to my surprise, you can change the mode any time you like, noting : "Switching is always allowed, but is valid from the next line" (32X hardware manual, VDP registers - Display mode selection)
thx
Image

Chilly Willy
Very interested
Posts: 2533
Joined: Fri Aug 17, 2007 9:33 pm

Post by Chilly Willy » Sat Jun 28, 2014 1:34 am

The MD display can be anything at all while the 32X display is off, but the 32X display can ONLY be on when the MD is in 320x224(240) mode. So you can't use the 32X display with a 256 wide MD mode. Interlace is unsupported by the 32X... no telling what happens. The MD timing isn't used, so I'd guess that you get a non-interlaced output with the MD flickering between two different displays.

Post Reply

Who is online

Users browsing this forum: No registered users and 2 guests