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52

A nice one - and coming up every now or then. TL;DR The Apple IIs video logic produces a B&W bitstream at the right frequency to bedazzle an NTSC TV set in a way to make it 'see' colour. The colours produced are based on the way the bitstream creates interferences that are detected by the TV set as colour information. The encoding is rather a series ...


35

CRTs don't have pixels, they don't work that way. Also, arcade monitors expose all the picture controls at the back so it is possible to adjust them quite extensively. Operators would have made sure that the picture was the right shape and in focus near the edges. Since the controls are all analogue and no-one bothered to measure the display geometry the ...


15

I think you're conflating a few issues: being in-phase with the colour subcarrier; being sampled at a rate less than or equal to the colour subcarrier; and being sampled at an integer division of the colour subcarrier. Being in-phase has exactly one effect: the artefacts on horizontal edges are consistent from one line to the next. The edges do not ...


14

Did arcade monitors have same pixel aspect ratio as TV sets? Short answer: No, not necessarily. Long Answer: To start with, 'Title Safe Area' is an idea to define the parts of one transmission to be displayed even if any of the many receivers is maladjusted. It's nothing inherent to the TV signal or its definition, it's a safeguard against less than ...


11

The pixel clock has to be fast enough to generate the number of pixels you want to display horizontally within the 56 microsecond scan line interval. At 3.58MHz, you only get about 200 pixels. This was fine for the Atari 2600 et al, which had 160 horizontal pixels, but the other systems you mentioned had higher horizontal resolution, so had to use a faster ...


10

A typical black and white television will be capable of displaying 80-column text that can be read, but such text will generally be sufficiently unpleasant to read that some other kind of display would be preferable. Among other things, a monitor which is adjusted to have extremely sharp focus and modulate the beam very sharply will generally produce a ...


10

The pixel clock doesn't have to be the same as the color clock. In fact, it's usually higher. Remember that in a composite video signal, the chrominance information (whose resolution depends upon the color clock) is less important than the luminance information (whose resolution depends upon the pixel clock), so the color clock can be (and usually is) slower ...


10

While nominally 241 scan lines were visible in the sense they contained video information, all TV sets hid a varying amount of scan lines on top and bottom (and left and right) by overscan and by the bezel in front of the screen. So with a vertical resolution of 240, on most TV sets parts at the top and bottom would not be seen. While this doesn't matter ...


10

Rather than convert the NES, just get a PAL monitor. The common auto backup video systems use an NTSC/PAL switchable monitor, available for not much money.Backup monitor 7" It is also possible, with some video capture cards, to select PAL (then your computer display will allow you to use the game). If your TV takes PAL input (some do: check all the ...


9

You'll have to get a PAL to NTSC converter. A modification to make a PAL NES to output NTSC video would be extremely difficult because both the console and the games are designed for the video signal. The NES's clock frequencies were chosen to match the timing of the video signal, so you'd have to replace the clock circuitry. The PPU is hard-wired to ...


9

It depends on whether the TV is color or black-and-white/monochrome. Older B&W TVs (and ordinary TV electronics and tubes converted into monochrome monitors by some el-cheapo monitor vendors), did not block (filter out) color burst frequencies (with the associated IQ bandwidth), and the cheap analog filtering did gracefully degrade as the bandwidth was ...


8

NTSC provides 227.5 colour cycles per line; PAL is very close to 283.75. In both cases, the visible area is around 80% of the line, but most home computers had a much bigger border than that — e.g. (of those I know offhand) the Acorn machines paint for 40µs, which is 62.5% of the line; the 48kb Spectrum paints for 128/224ths, which is around 57%; over in ...


8

Short Answer: There is no relation. What seems like a relaiton is non related coincidence. Long Answer: First of all, there is no colour clock. The mentioned frequency of 3.58 MHz is not a colour clock, but the carrier frequency used to modulate the encoded colour signal atop the basic B&W signal. There is no relation to RAM speed, pixel generation ...


8

Yes, but only a very slightly different speed: the master crystal was around 14.238Mhz rather than 14.31818Mhz. which is only around 0.5% different, so I would expect safely within tolerance for a Disk II. Something PAL users didn't get from the base machine: colour. The relationship with phase is a lot more complicated in PAL, as that's how the error ...


8

TLDR: It's a soft spot for optimization around the ability to display 25 lines of text. (And why this is important has been discussed some time ago in an answer to your question about why 80x25 became standard) Preface: As usual with such decisions there are many factors involved - and most of them are not hard but variable within a certain frame and in ...


7

The V9938 video chip in the MSX2 home computer can be programmed to disable the color burst but I don't know if any utilities or applications provided such an option to the user. That would have certainly been beneficial for the 80 column text mode and 2-color high resolution bitmap mode. Some MSX2 variants had a V9958 instead which has no composite video ...


7

Asteroids is an example of an arcade cabinet that didn’t even use raster graphics, but vector graphics. Battlezone and Lunar Lander were others. They used similar technology to the Tektronix 4000-series terminals of the ’70s, or the IBM 2250: A cathode ray fired into the back of a glass screen coated with phosphors, like in an old-fashioned black-and-...


6

At startup, the Amiga used a timing routine to check the frequency of the AC power supply, and start in PAL (50 Hz AC) or NTSC (60 Hz AC) appropriately. Unfortunately, the detection was buggy, and sometimes 50 Hz was wrongly identified as 60. Many Europeans would have Declan McArdle's NoPALReset in their s:startup-sequence to avoid this. I think the problem ...


6

I'm not sure if I understand the question correctly. TV composite is bandwidth limited because the color carrier signal blocks higher frequency. This means one particular type of signal cannot "gracefully degradate": If the horizontal resolution is too high, you'll just get colored jumble on the TV, and not somehow a fuzzy image in lower resolution. RF ...


6

The simplest way to think about composite video on the Apple is to imagine that vertical colored stripes of red, blue, and green, and yellow are overlaid onto the picture. These strips are half a pixel wide in hi-res mode, and 1/14 pixel wide in lo-res mode. If memory serves, when the upper bit of a byte is clear, half the pixels will hit the red and blue ...


6

No, not quite like that. Nobody pointed out to you that the pixel bits are stored in reverse order. 0 00 01 10 1 -> 0 1 01 10 00 = 58 1 1 00 01 10 -> 1 01 10 00 1 = B1 How can you see what it looks like? You could do it like this: HGR CALL-151 2000:58 B1 N 2002<2000.3FF6M But then you'd see it doesn't look like what you expect, so I wrote you a ...


6

The Apple II Reference Manual (Apple product number A2L0001A), published in 1979 by Apple Computer, Inc. for the Apple II and Apple II Plus computers, contains a few pages about the end-user data format of the high resolution graphics mode: Each dot on the screen represents one bit from the picture buffer [a dedicated 8K region of memory]. Seven of the ...


6

I had two micros when I was growing up: the SAM Coupé and the Acorn Electron. The SAM Coupé has a 512x192 mode much like you discuss. It actually makes the display physically wider than a Spectrum though, pixels being approximately 1.25 times as wide as tall. The Acorn Electron inherits full 80-column 640x256 video from its progenitor, the BBC Micro. In ...


4

I once owned a black and white monitor (not sure if it was a computer monitor or CCTV monitor) that I hooked up via composite to a CGA card, and 640x200 (enough for 80 columns) was very sharp. But while it was NTSC, technically it wasn't a television in the normal sense, and if you hooked up through RF, I think you would not be very pleased with the results.


4

Not sure if you should call it an advantage, but the Apple II used the double color clock frequency to create colors. Consider two bit patterns, 0101010101 1010101010 On a monochrome display, they represent just a dotted pattern. On a color display, you have a signal with the frequency of the color clock, but with a different phase. And the phases produce ...


4

I can think of several options: The hardest one (because it is still WIP) is to remove the PAL ULA and get a NTSC ULA. NTSC ULA's existed for some clones intended for the American market. Today they are very rare chips. However, there are some projects that aim to design a direct replacement ULA using programable logic. These projects may support NTSC ...


4

It'd depend on your TV. Some may just show 240 lines, of course, but assuming yours is chopping off only eight in total, that leaves 232 visible. It looks like the NES scans at 63.5us per line, which is exactly to spec per NTSC, to fit 240 lines, each would need to be slightly less than 61.4us — 232/240 as long as 63.5, or a 3.33% digression from the ...


4

Yes and no. Yes, you can play with the signal timing, but if you do it won't be NTSC video anymore, it will be something kind of similar to NTSC but with different timing. This means you might not be able to display your signal on an NTSC monitor (or you may damage your monitor attempting to do so). There were some NTSC monitors that had a switch setting ...


4

I used several B&W television sets as 80 column monitors "back in the day" with acceptable results, but I always modified them to bypass all the RF stages. This required finding a point to inject the video signal into the video amplifier input. One problem was that virtually all B&W sets are "hot chassis", meaning that the AC power cord is connected ...


4

Simple answer: Yes, they all do (plus many US HDMI TVs accept 50 Hz anyway). But you may want to check if they are able to process PAL input, as there are some (usually older) who don't. Also, there are differences in their upscaling algorithms, so while this is no big issue for a movie it might be annoying on certain consoles/games. So it might help to ...


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