• From: England
  • Registered: 2017-04-24
  • Posts: 65

Topic: Non Interlaced PAL fields

As the post title sounds contradictory, what I'm referring to is using 720x576i however rather than one of the fields starting offset by half a line, both fields start with the same offset. Causing both fields of 288 lines to overlap. In effect reducing the resolution down to 288p.

From what I can gather the Acorn Electron in mode 0 uses 640x256 PAL @50Hz. With the above change and using the center 512 lines for display of the 576 available, a 640x256p @ 50Hz could be achieved.

Is that what the actual Electron did?

If it's not clear what I'm asking, it's described on the rigacci site in the Non interlaced modes section.

I think at the moment, the 576i mode outputs the 2nd field offset by 1/2 a scanline so that interlacing occurs. Would it be possible to add a 256p mode and tweak the VideoTiming module to accommodate it?

hicks's Website

  • From: England
  • Registered: 2017-04-24
  • Posts: 65

Re: Non Interlaced PAL fields

I believe I have this sorted now. I've added a new set of timing information and made a minor tweak to the VideoTiming to support a PAL_P mode which allows for the slightly different cs_gate requirements.

Once I've got the core as far as rendering more than a filled screen and verified this works I'll add the core+this change to svn.

For now I've duplicated the VideoTiming + Pack locally to the core so my modifications have no impact on any other core.

hicks's Website

  • MikeJ
  • Administrator
  • Offline
  • Registered: 2011-05-05
  • Posts: 2,573

Re: Non Interlaced PAL fields

Sounds fantastic. I completely broke myself at Glastonbury but I'm on the mend now....