Interlace?

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
Post Reply
VinCBR900
Posts: 12
Joined: Wed Jul 27, 2011 8:21 pm
Location: San Diego, CA, USA

Interlace?

Post by VinCBR900 »

I tried a Google search and kept coming up with Speccy links, but has anyone managed an interlace Hi Res graphics mode on the zeddy?

I thought about Two H files in lower 32k ram , switching I register on alternate video frames during vblank with 1/2 video scan line delay on secodn h file to offset?

Alternatley, same vide scan line offset for each H file but with some pixels missing on second H file to achieve pseudo gray?

Comments?
User avatar
Andy Rea
Posts: 1606
Joined: Fri May 09, 2008 2:48 pm
Location: Planet Earth
Contact:

Re: Interlace?

Post by Andy Rea »

yeah it's been tried, but in my opion the milage varies depending on what display hardware your using.

25thanni has a secret hidden part that display an image of ZX81 thats supposed to have grey.

rezzurection demo also has interlaced display in final part.

and there was (but i can;t find it) a sliding puzzle game that did interlace.

getting the zeddy to output Vsync is no problem, but you have to remember that contrary to popular belief the hsyncs are not reset by the Vsyncs, they are reset by int Ack. so you need to time your Vsync pulse to the last int, hsync happen every 207 cycles unless reset by another int Ack. so getting the half a line swithc between vsync and hsync is gonna be a pain. but not inpossible.

HTH

Andy
what's that Smell.... smells like fresh flux and solder fumes...
VinCBR900
Posts: 12
Joined: Wed Jul 27, 2011 8:21 pm
Location: San Diego, CA, USA

Re: Interlace?

Post by VinCBR900 »

I would have been surprised if no one else had tried this in 30 years.

Bodo's page is very interesting with gray scale, 320 by 256 pixel display and also his CPLD ULA replacements.
Post Reply