Michael J. Mahon wrote: > > > No, the Apple II video is 60 fps, non-interlaced. > > I do not agree with this. NTSC is 30 frames per second, in two fields. 60 fields per second where each field is every other scan line. If the Apple did not agree with this format you could not use a TV as a monitor, with or without a modulator. I used it with a TV and modulator for many years, so I am certain of this. Perhaps you have some sort of video card which is different. > > The vertical scan rate does not determine the bandwidth required-- > it determines the number of horizontal lines. > If you assume that the number of scan lines are the same, at 60 frames per second you have half the time for each scan line. To have the same horizontal resolution you have to double the bandwidth. Or are you saying that the number of lines is cut in half at 60 fps? You have a 262 scanline monitor? It must be made by HP. It might be worth pointing out that NTSC is 30 frames per second. When you change the frame rate you are no longer NTSC compatible, strictly speaking. So if the frame rate changes I wouldn't be surprised if the number of lines was also changed, but these are arbitrary decisions made by the equipment manufactuer. OK, I looked up NTSC. A scan line 63.5 usec. The line rate is 15750 scan lines per second. A screen is 525 lines. So 15750 / 525 = 30 frames. The horizontal blank is 0.16 of the line duration, so the picture has (0.84)(63.5 usec) = 53.4 usec for the line. If you have 7 pixels per character, and 80 characters per line, then you need a resolution of 560. 53.4 usec / (560/2) = 0.1907 usec, or about 5.25 MHz. This would be an absolute bare minimum. If everything else is the same (525 lines) but you double the frame rate the time per pixel would be cut in half. You would need 10.5 MHz. Which agrees with your previous range of 10-14 MHz. (You need to give some extra bandwidth or you may get some interference from adjacent pixels, plus transition bands for the filters) > > Don't worry--all 80-column cards produce frame rates which are > well within the lock range of a nominal 60Hz monitor. And all that > I know of use non-interlaced video, since the display of characters > with single-line features creates annoying flicker if an interlaced > display is used without an unusually long-persistence phosphor. > I'm not worried at all. It is possible that the flicker is a problem. Interesting that it was never an issue at 40 columns on an interlaced display. But I think TVs have longer persitance than the typical monitor. I should look up the actual video circuit. The Apple had something line 192 rasters so you should get more than 2 scan lines per pixel. Maybe that had something to do with it. Big fat blurry pixels. It amazes me how much these guys did with not much more than TTL. David Stark replied: >Michael J. Mahon wrote: > >> No, the Apple II video is 60 fps, non-interlaced. > >I do not agree with this. NTSC is 30 frames per second, in two fields. > 60 fields per second where each field is every other scan line. If >the Apple did not agree with this format you could not use a TV as a >monitor, with or without a modulator. I used it with a TV and modulator >for many years, so I am certain of this. Perhaps you have some sort of >video card which is different. > >> >> The vertical scan rate does not determine the bandwidth required-- >> it determines the number of horizontal lines. >> > >If you assume that the number of scan lines are the same, at 60 frames >per second you have half the time for each scan line. To have the same >horizontal resolution you have to double the bandwidth. Or are you >saying that the number of lines is cut in half at 60 fps? You have a >262 scanline monitor? It must be made by HP. That is exactly what I mean. Any scanned interlaced monitor displays only 262.5 lines per field, with the 525 lines resulting from the fact that the second field is scanned in between the lines of the first--or displaced by 0.5 line of the 262.5-line field. Interlace is not a property of scanning frequencies. It is a consequence of the timing of the vertical sync pulse. If the vertical sync pulse occurs at an odd multiple of half the line scan period (like 262.5) then the display is interlaced. If the vertical sync pulse occurs at a multiple of the line scan period, then successive fields' lines exactly overlap, and the display is non-interlaced. The Apple II display is 262 lines, refreshed 60 times per second, and any NTSC-compatible scanning monitor can do that. >It might be worth pointing out that NTSC is 30 frames per second. When >you change the frame rate you are no longer NTSC compatible, strictly >speaking. So if the frame rate changes I wouldn't be surprised if the >number of lines was also changed, but these are arbitrary decisions made >by the equipment manufactuer. > >OK, I looked up NTSC. A scan line 63.5 usec. The line rate is 15750 >scan lines per second. A screen is 525 lines. So 15750 / 525 = 30 frames. > >The horizontal blank is 0.16 of the line duration, so the picture has >(0.84)(63.5 usec) = 53.4 usec for the line. If you have 7 pixels per >character, and 80 characters per line, then you need a resolution of >560. 53.4 usec / (560/2) = 0.1907 usec, or about 5.25 MHz. This would >be an absolute bare minimum. In the Apple II, to allow for overscan common in TV monitors, only 40 microseconds of each line are used for display. Since you are correct that 560 pixels are needed for the 80-column display, the dot clock is 14.3MHz, as I stated. BTW, only 192 of the 262 lines are used for display on the Apple II, also to deal with overscan. There has never been an 8-bit Apple II that was capable of more than 192 lines of native resolution. (There have been some add-on cards that increased it. For example, the Video Overlay Card generates both 525-line interlaced video or 200-line SHR, like the IIgs.) >If everything else is the same (525 lines) but you double the frame rate >the time per pixel would be cut in half. You would need 10.5 MHz. >Which agrees with your previous range of 10-14 MHz. (You need to give >some extra bandwidth or you may get some interference from adjacent >pixels, plus transition bands for the filters) Only if you double the number of lines in a "field". As long as there are only 262 lines being refreshed in 1/60th of a second, doubling the number of lines by interlacing doesn't affect the bandwidth. That is the entire motivation for interlacing in the first place--to increase the vertical resolution without increasing the bandwidth. >> Don't worry--all 80-column cards produce frame rates which are >> well within the lock range of a nominal 60Hz monitor. And all that >> I know of use non-interlaced video, since the display of characters >> with single-line features creates annoying flicker if an interlaced >> display is used without an unusually long-persistence phosphor. >> > >I'm not worried at all. It is possible that the flicker is a problem. >Interesting that it was never an issue at 40 columns on an interlaced >display. But no Apple II video _is_ interlaced--look it up if you don't want to believe me. ;-) > But I think TVs have longer persitance than the typical >monitor. I should look up the actual video circuit. The Apple had >something line 192 rasters so you should get more than 2 scan lines per >pixel. Maybe that had something to do with it. Big fat blurry pixels. > It amazes me how much these guys did with not much more than TTL. You are confused. Read my description of Apple II video above, or look it up for yourself. The Apple II video generation is, indeed, a nice engineering job. The cleverest parts were getting artifact NTSC color for "free" by playing with the clock frequency and phase, and using the video refresh cycle to simultaneously refresh the DRAMs. -michael Check out amazing quality sound for 8-bit Apples on my Home page: http://members.aol.com/MJMahon/ Michael J. Mahon wrote: >> The other issue is if the 80 columns are interlaced or not. The >> standard composit output from the Apple is 30 frames (not 60) >> interlaced. > > No, the Apple II video is 60 fps, non-interlaced. No. NTSC video is 30 frames per second interlaced, which works out to 60 FIELDS per second. The reference to 60 fields per second (an interlaced frame consists of two fields) is probably what inspired the earlier poster's correction. Apple II video is NTSC video, because it can be output to any NTSC composite, or monochrome monitor. And I use the term "NTSC monochrome" advisedly, to indicate 525-line, 30-frame-per-second, interlaced monochrome video. I would also use the term "PAL monochrome" in the same context to indicate 625-line, 25-frame-per-second monochrome video. Of course, we could always adopt HD nomenclature, and say 525/60i and 625/50i. HDTV terminology deals with the smallest vertical refresh unit, which is a frame in progressively scanned video, but a field in interlaced video, and indicates the method of scanning used as the last character, so a progressively-scanned image at the same resolution and frame rate would be 625/30p. In article , Kelli Halliburton wrote: >Michael J. Mahon wrote: >>> The other issue is if the 80 columns are interlaced or not. The >>> standard composit output from the Apple is 30 frames (not 60) >>> interlaced. >> >> No, the Apple II video is 60 fps, non-interlaced. > >No. NTSC video is 30 frames per second interlaced, which works out to 60 >FIELDS per second. The reference to 60 fields per second (an interlaced >frame consists of two fields) is probably what inspired the earlier poster's >correction. > >Apple II video is NTSC video, because it can be output to any NTSC >composite, or monochrome monitor. Some versions of the Apple II could be hardware strapped on the motherboard though, to produce 625-line 50 fields/sec video, which was monochrome unless a PAL card was inserted in Slot 7. >And I use the term "NTSC monochrome" advisedly, to indicate 525-line, >30-frame-per-second, interlaced monochrome video. I would also use the term >"PAL monochrome" in the same context to indicate 625-line, >25-frame-per-second monochrome video. Of course, we could always adopt HD >nomenclature, and say 525/60i and 625/50i. The latter is definitely preferable, since the term "PAL monochrome", (besides being an oxymoron) would be confusing to someone from e.g. Brazil, a country which uses 525-line 60 frames/s PAL for its national TV transmissions. >HDTV terminology deals with the smallest vertical refresh unit, which is a >frame in progressively scanned video, but a field in interlaced video, and >indicates the method of scanning used as the last character, so a >progressively-scanned image at the same resolution and frame rate would be >625/30p. > > -- ---------------------------------------------------------------- Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN e-mail: pausch at stockholm dot bostream dot se WWW: http://www.stjarnhimlen.se/ http://home.tiscali.se/pausch/ Kelli Halliburton wrote: >Michael J. Mahon wrote: >>> The other issue is if the 80 columns are interlaced or not. The >>> standard composit output from the Apple is 30 frames (not 60) >>> interlaced. >> >> No, the Apple II video is 60 fps, non-interlaced. Actually, David Stark wrote the >>> part. I wrote the >> part. And 60 fps in the case of non-interlaced video is "frames", since for non-interlaced video there are no "fields" (or the field is identical to the frame). >No. NTSC video is 30 frames per second interlaced, which works out to 60 >FIELDS per second. The reference to 60 fields per second (an interlaced >frame consists of two fields) is probably what inspired the earlier poster's >correction. > >Apple II video is NTSC video, because it can be output to any NTSC >composite, or monochrome monitor. Apple video is _close_ to NTSC, in the sense that it will work with an NTSC-compatible monitor, but it is _not_ NTSC, since it is non-interlaced. It also differs from the NTSC standard in its blanking and sync pulse timing--it's just "close enough" to work on almost anything that NTSC works on. >And I use the term "NTSC monochrome" advisedly, to indicate 525-line, >30-frame-per-second, interlaced monochrome video. I would also use the term >"PAL monochrome" in the same context to indicate 625-line, >25-frame-per-second monochrome video. Of course, we could always adopt HD >nomenclature, and say 525/60i and 625/50i. > >HDTV terminology deals with the smallest vertical refresh unit, which is a >frame in progressively scanned video, but a field in interlaced video, and >indicates the method of scanning used as the last character, so a >progressively-scanned image at the same resolution and frame rate would be >625/30p. I agree that this is the standard terminology. The OP's major error was in thinking that the Apple II video was interlaced, which it is not. -michael Check out amazing quality sound for 8-bit Apples on my Home page: http://members.aol.com/MJMahon/