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Realistically you'd want 2 character heights additional top and bottom of the default text screen to cater for games, demos and software you're likely to come across. The system can actually do 3 character heights top/bottom additional to the default (6 total = 30 for 240 scanlines) Generally it's demos that will use a lot of the potential screen area where games will be a bit more conservative. On PAL - IMO there's no reason really to not have the entire 240 scanlines visible and most CRTs will be that way.
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The usual case with NTSC is that there's no non-display in the vertical plane. With PAL we usually see at least just under a character height worth at top and bottom. (use SE. 4,3,4 to set a border colour first so you can clearly see the offscreen areas) Also the usual with NTSC was that you'd lose at least part of the first character (and also often with PAL) - that's why we have the 2 character margin (which probably could be just 1 for 99% of cases) Plus/4 has almost identical default screen architecture though I think their character start is slightly to the right vs ours. If you have an adjustable monitor I'd advise leave a couple of pixels at left/right for border. The usually always black nondisplay at top/bottom, similar though you want to leave a little more top/bottom with PAL. In most cases games didn't really use the display outside the normal 320 horizontal though in some cases it can be useful to see a bit more. All that said though, if you differ too much from your video system's norm, you might end up with an aspect ratio that you're not used to.
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Using Interlacing For Double Vertical Resolution
Rybags replied to pcrow's topic in Atari 8-Bit Computers
It doesn't actually - same as most old computers and consoles. The Amiga by default does progressive but also has an interlaced mode. The video signal isn't broadcast standard but old TVs would handle it just fine. The interlace is generated because there's a HSync pulse inserted halfway through a scanline which offsets the vertical sawtooth wave by 1/2 a scanline on the following field. Progressive mode displays don't do that. -
Optimization for speed/efficiency BASIC XE
Rybags replied to Ricky Spanish's topic in Atari 5200 / 8-bit Programming
Probably some gain to be had by stacking statements on a line rather than just 1 per line. Possibly reordering so that the main loops are closer to the start though I think Basic XE doesn't suffer the same bad search speed for branches that Atari Basic does. Where there's complex calculations - if there's stuff like integer multiplies on a sequence of numbers in a loop you can often get speed gain by just precalculating and storing the results in an array for later reference. -
Using Interlacing For Double Vertical Resolution
Rybags replied to pcrow's topic in Atari 8-Bit Computers
There's a hardware bug/exploit which allows simulating the interlaced signal. Just alternating the 2 frames isn't sufficient, you also need the code that generates interlace. Though some modern LCDs will do interlace regardless but you shouldn't rely on that to always be the case. -
Alternate History: What Atari Could Have Done Differently?
Rybags replied to pcrow's topic in Atari 8-Bit Computers
800 should have been more open architecture, as in slots closer to PBI capability. 400 probably would have been better done XEGS style with keyboard optional later purchase on a low end model. XL needed to be sooner. They could have gone single board for the huge production saving cost probably by mid 1981. Amiga - instead of dealing with them and slipping a loan for their chipset they'd have done better to just purchase the company outright. ST - the release spec of the ST should have been the STe - as in DMA sound, blitter, fine scrolling and 4096 colours at the least. That way it would practically match the Amiga. Falcon - needed to be sooner and needed to be full 32-bit. Jaguar - maybe hold off release at bit and do it as a CD system from the onset. -
Enabling the VBXE just puts the emulated hardware there but does nothing relating to the driver or software side of things. To use such things as the 80 col E: device etc you'd need a suitably setup Dos environment that loads the required drivers.
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Check for presence of certain data in known locations? Though if you're not using MEM.SAV you could potentially have most of DUP.SYS present in Ram after it has been exited. Unless there's some flag byte somewhere then it mightn't be possible. Does DOSVEC retain the same value in a no BASIC situation whether DUP.SYS is in memory or not? And all that said, what works for Dos 2.x won't necessarily be good for 3rd party Doses.
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Possible bad antic socket or 4050 chip/socket on a pal 800xl
Rybags replied to Beeblebrox's topic in Atari 8-Bit Computers
Re the vertical bar. Can you try in Basic - try POKE 704,54 then also try locations 705 thru 707 - just to confirm it's a PM object there. If the GTIA is good, then maybe it's Antic with a problem. That text effect is just weird. -
Possible bad antic socket or 4050 chip/socket on a pal 800xl
Rybags replied to Beeblebrox's topic in Atari 8-Bit Computers
Might be GTIA going bad. Weird - it's the normal blue screen but that text looks like it's in a GTIA mode. Does the computer otherwise work normally? -
Possible bad antic socket or 4050 chip/socket on a pal 800xl
Rybags replied to Beeblebrox's topic in Atari 8-Bit Computers
Rule out 4050 from GTIA - it's just buffering the LUMA outputs before the video mixing. The vertical line is probably a PM object. On powerup you'll often see lines like that which disappear after a second. Seeing them with the normal E: screen is strange and could suggest bad OS, RAM, 6502 or some sort of corruption occurring to program data as it executes. -
Possible bad antic socket or 4050 chip/socket on a pal 800xl
Rybags replied to Beeblebrox's topic in Atari 8-Bit Computers
Maybe check OS Rom and MMU. Try a diag mode game cart such as Asteroids or Star Raiders. -
All PAL XL/XE use 2 crystals. AFAIK every Freddie equipped computer should use a 14~ MHz master crystal. The 4.43~ MHz one is exclusively used to generate the colourburst as it can't be directly derived from the others. It's a mystery to me why anyone with reasonable Atari knowledge would attempt to use a slower crystal in place of the 14 MHz one. The smaller clock divisions are needed since Freddie also does the RAS/CAS sub-cycle operations which otherwise would have been accomplished with help from the delay line which it replaces among other things.
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There can be issues when the browser might try to open the file instead of offering to save it. In Firefox at least you can change the action in settings (ask, save, open in Firefox, use default Windows application etc)