Actually, I screwed up the math. You don't want a crystal that's 1.5 times the color burst, but one which, when multiplied by a multiple of 1.5 and divided by a power of two gives you that frequency. So 4/3 x 4.43 = 5.906666 MHz. That way, frqa will have two one bits in succession, with the rest being zeroes.
-Phil
Or, on the topic of special PAL frequencies, maybe this one :
4.987821MHz - that gives /18.000 for PAL Chroma, and /13.000 for PAL pixel clock , and should be close enough to 80MHz for most other apps ?
( 0.243% ? )
Why NTSC? To make a profit, i.e. the benefit (in increased sales) was believed to justify the cost to develop & include it. I suspect the decision path went something like:
1. There is great value to a microcontroller if it can generate a display with minimal external circuitry. Serial ports and LCD displays are workable, but there is great value-add in being able to connect an off-the-shelf display.
2. While it is possible to generate a TV signal using only software (i.e. bit-banging), there's a lot of difficulty and limitations because of timing and frequency constraints. Adding the PLL and the video generator makes it possible to generate VGA output at a variety of resolutions. These same circuits can be leveraged for other purposes.
3. Once the video generator has been implemented, the addition of the phase generation circuit for composite video is fairly simple and significantly increases the number of usable displays.
Analog TV also has some benefits over VGA in that it only requires a single conductor and is very tolerant of out-of-spec signals. (Yes, PAL does have issues with phase jitter, but feed a CRT NTSC TV something which is close to composite video and you will likely get something.)
HDMI has four differential pairs - a clock pair which is at the pixel clock rate (i.e. 25MHz) and three data channels (typically RGB) which run at 10 times the pixel clock rate (one 8 bit pixel per channel per clock, encoded as 10 bits). So to generate HDMI the Propeller would need to be able to encode and shift out the pixel data at ten times the rate it does for 640x480 VGA. Not possible without a lot more circuitry.
I have a few boards and devices that can output NTSC and/or PAL. Fortunately they can also output VGA, because in practice I can't see how TV output could possibly be useful until just recently, when those cheap small car reverse displays started showing up.
I don't know about you guys, but I only have a single TV, and it's in the living room, and it's big and far away from tables and chairs. There's no way I can connect anything to it.
VGA displays on the other hand are everywhere, and they're on a table where I can conveniently use a chair and sit down with my board and a short cable. Instead of sitting 6 metres away with a seriously long cable and having other people in the living room trying to strangle me with said cable.
Back in the seventies TV output was a) the only possibility for home use, and b) you could and would buy small TVs. To buy a TV today, for use with a dev. board.. who would do that? In shops you'll find only 40" TVs and upwards. VGA displays are cheaper and can be bought in small sizes. At work they're getting dumped all the time anyway (because everyone is changing to larger screens as they become cheaper) so in practice they're free.
So, I can understand that it's cheap and simple to add NTSC support to e.g. the propeller, but was there really any point? Until recently, I mean. Because now it suddenly _is_ useful, due to those cheap small LCD screens with PAL and NTSC support - but they didn't exist when TV output was added to at least those boards I own. So it's always looked pretty useless to me, and a waste, however cheap it's to add.
Tor,
You only have one TV in the house. Same here. And the same for pretty much every european famy I have ever known.
Perhaps that's the thing, I have an image in my mind that a lot of Americans are living in bigger houses than Europeans and tend to have a lot of TVs spread throughout the house.
Video capture cards are fantastic. You can put a window on your screen with prop output on it. I do it constantly. Laptops don't have VGA in. One would think this feature would be found in a machine or two, but it isn't. The TV out is quick 'n easy, frame and movie captures too.
Used a real TV for a small amount of time, then got a USB capture shortly afterword. Again, the circuits as mentioned above are not complex, not expensive, and have many uses beyond video. IMHO, that's the brilliance behind how it really is done on the Prop. A full on graphics system would have cost more silicon, would very likely not have seen all the uses we've seen, and it's capability would have been more limited than we've seen as well.
And I don't know about where you live, but TV's of all sizes are easily found, and have been for some time. They are cheap to free.
One other thing about TV and that's the lower sweep frequencies. VGA used to have a nice 15Khz horizontal sweep, but not any more. Few devices will render that signal, forcing the use of higher sweeps. Where that's true, higher dot clocks are needed as well, which limits what the chip can do overall.
For development, it's a great debug display too. Serial works, but has limits. You can put all sorts of data on a TV, and do so in many forms, and it's high bandwidth, able to display a lot, and do so in parallel, where serial isn't so fast, and sequential.
Because it's not a serious cost, it can be completely ignored too. Chip came from the time when TV displays made a lot of sense, as did the simple old methods. Was a no brainer to add.
Lots of good points, IMHO, just differences in hardware availability.
The very first thing I did was blink the LED. The second was to hook up the TV and start doing stuff.
For the "pro", we've had this discussion many times. People see 8 video generators and see waste. However, they also have seen that stuff put to all kinds of uses, and again, it's not a big deal cost / silicon wise, as the CPU does most of the work. Really, the circuits add the color signal, and buffer the bit streaming, greatly extending what the chip can do for almost nothing.
I guess the question really would be, why not include it? If the waitvid function were there for VGA, which it would be right? Why not do NTSC? In fact, if it's there for VGA *at all*, then NTSC can be done, with the only real impact being the need to software generate chroma. The feature benefit significantly exceeds the very minor silicon cost.
I think Heater is on to something. It must be a European/American, or cultural difference. Over here a TV simply isn't available for just connecting devices. Even though there are these days often more than a single TV in homes, the TVs in the kid's room would still be a big one which you can't just sit down in front of and hook up your short cable. No table, no chair, not nothing. Utterly inconvenient. Two of my gadgets came with 3 metre long cables, they're not getting any use either - way too short. No kid would be seen with, say, a 30 inch tiny TV either, so small TVs are in vast minority in shops too.
It's quite baffling. Everything seems simpler than to use a TV. However, what potatohead said about video capture cards.. now that's interesting. If that could be used to connect some TV out, or at least S-video or composite to a laptop.. that would be convenient. Must look into that.
Of course there is the slight inconvenience that I have never bought a TV in my life. Lived for 14 years without one at all. No time for that during uni and later.
Turns out women cannot live without TV so there has been one around for a long time. But then it is in the control of "Her indoors":)
Getting a small, cheap, TV just for hobby experiments is expensive. Small old TVs are impossible to find around here.
I also learned about TV when at school, among many other (useful) technical things . I'm glad I did not waste my time with bookkeeping and such stuff (taught at others schools). TV is a marvel, sadly programming does it little to no justice !
OMG, I had never considered using a computer video capture card to take a display from a Prop's NTSC/PAL and then doing a screen capture to save the image.
Currently, I have an outboard TV box that feeds into a VGA share with my old XP, but I have considered putting a card in the computer and many do come with video capture. I've just thought that it was better to conserve the electricity when watching TV by not having a computer on.
Thanks. This makes a lot of Propeller projects available with less clutter around the computer.
You can find this forum littered with captures I've done. My favorite mode is to run a 64 column display, color in my blog (80x50) for a resident text mode screen I can just output results to. I do a fair amount of business travel, and I take some prop stuff, the capture and a laptop or two, because my prop stuff is just nice to have setup on a older laptop.
The only downside I've run into is many of the viewer programs that come with capture devices introduce up to a second of latency. Often the "Preview" window in many movie authoring programs won't have it, or will have a fraction of that latency. So don't game on one.
When it comes to NTSC / PAL / Composite / S-video, capture cards are great! It's possible to sync your average laptop display to 50 / 60Hz, working reasonably with both standards. Ordinary definition capture cards perform reasonably well on a composite signal, and excellent on a s-video one. High definition capture cards (recommended) perform considerably better on composite, just FYI.
Re: Euro / American differences. I agree with those. The US has TV's all over the place. You can get them for nothing, and it's not hard. Big ones, little ones, extra ones, etc... And we fill them with absolute Smile most of the time too. Never did get it, but then again, I'm not your usual US fare, only watching a few hours per week tops. (Half that is on the Beeb anyway)
We even stuff TV's in our cars now, one of the primary reasons I drive older vehicles. Can't stand all the gadgets in the car! It's very common to see families with their kiddies plugged into something in the back seat, instead of actually experiencing the drive... I much prefer car talk and games. Deffo older school in that regard.
Growing up, I did TV repair in high-school for date money. Would do alignments too. Used my Atari for that, as it could generate most of the useful patterns and color references. Not a "pro" quality signal, but plenty good enough to align a TV for a great picture. Not so necessary today, but back then component aging really had a impact. A "factory fresh" look faded after, say 5 years. A readjustment usually brought that back, and I could get $20-50 a pop on those, angering the local TV guy, who wanted to see that "new fangled" computer thingy! A Prop does most of that today, minus the greys without some tricky programming, and can output a variety of signal variations as well! Damn cool. Interlaced, non, color phase change, non, full frame, overscan border, etc...
LOL@Heater: So true! Well, mine will also game with me, and at least "ooh" and "ahh" on the projects. I'm happy!
Comments
Or, on the topic of special PAL frequencies, maybe this one :
4.987821MHz - that gives /18.000 for PAL Chroma, and /13.000 for PAL pixel clock , and should be close enough to 80MHz for most other apps ?
( 0.243% ? )
1. There is great value to a microcontroller if it can generate a display with minimal external circuitry. Serial ports and LCD displays are workable, but there is great value-add in being able to connect an off-the-shelf display.
2. While it is possible to generate a TV signal using only software (i.e. bit-banging), there's a lot of difficulty and limitations because of timing and frequency constraints. Adding the PLL and the video generator makes it possible to generate VGA output at a variety of resolutions. These same circuits can be leveraged for other purposes.
3. Once the video generator has been implemented, the addition of the phase generation circuit for composite video is fairly simple and significantly increases the number of usable displays.
Analog TV also has some benefits over VGA in that it only requires a single conductor and is very tolerant of out-of-spec signals. (Yes, PAL does have issues with phase jitter, but feed a CRT NTSC TV something which is close to composite video and you will likely get something.)
HDMI has four differential pairs - a clock pair which is at the pixel clock rate (i.e. 25MHz) and three data channels (typically RGB) which run at 10 times the pixel clock rate (one 8 bit pixel per channel per clock, encoded as 10 bits). So to generate HDMI the Propeller would need to be able to encode and shift out the pixel data at ten times the rate it does for 640x480 VGA. Not possible without a lot more circuitry.
I don't know about you guys, but I only have a single TV, and it's in the living room, and it's big and far away from tables and chairs. There's no way I can connect anything to it.
VGA displays on the other hand are everywhere, and they're on a table where I can conveniently use a chair and sit down with my board and a short cable. Instead of sitting 6 metres away with a seriously long cable and having other people in the living room trying to strangle me with said cable.
Back in the seventies TV output was a) the only possibility for home use, and b) you could and would buy small TVs. To buy a TV today, for use with a dev. board.. who would do that? In shops you'll find only 40" TVs and upwards. VGA displays are cheaper and can be bought in small sizes. At work they're getting dumped all the time anyway (because everyone is changing to larger screens as they become cheaper) so in practice they're free.
So, I can understand that it's cheap and simple to add NTSC support to e.g. the propeller, but was there really any point? Until recently, I mean. Because now it suddenly _is_ useful, due to those cheap small LCD screens with PAL and NTSC support - but they didn't exist when TV output was added to at least those boards I own. So it's always looked pretty useless to me, and a waste, however cheap it's to add.
-Tor
You only have one TV in the house. Same here. And the same for pretty much every european famy I have ever known.
Perhaps that's the thing, I have an image in my mind that a lot of Americans are living in bigger houses than Europeans and tend to have a lot of TVs spread throughout the house.
So, it boils down to a cultural expectation.
Used a real TV for a small amount of time, then got a USB capture shortly afterword. Again, the circuits as mentioned above are not complex, not expensive, and have many uses beyond video. IMHO, that's the brilliance behind how it really is done on the Prop. A full on graphics system would have cost more silicon, would very likely not have seen all the uses we've seen, and it's capability would have been more limited than we've seen as well.
And I don't know about where you live, but TV's of all sizes are easily found, and have been for some time. They are cheap to free.
One other thing about TV and that's the lower sweep frequencies. VGA used to have a nice 15Khz horizontal sweep, but not any more. Few devices will render that signal, forcing the use of higher sweeps. Where that's true, higher dot clocks are needed as well, which limits what the chip can do overall.
For development, it's a great debug display too. Serial works, but has limits. You can put all sorts of data on a TV, and do so in many forms, and it's high bandwidth, able to display a lot, and do so in parallel, where serial isn't so fast, and sequential.
Because it's not a serious cost, it can be completely ignored too. Chip came from the time when TV displays made a lot of sense, as did the simple old methods. Was a no brainer to add.
Lots of good points, IMHO, just differences in hardware availability.
The very first thing I did was blink the LED. The second was to hook up the TV and start doing stuff.
For the "pro", we've had this discussion many times. People see 8 video generators and see waste. However, they also have seen that stuff put to all kinds of uses, and again, it's not a big deal cost / silicon wise, as the CPU does most of the work. Really, the circuits add the color signal, and buffer the bit streaming, greatly extending what the chip can do for almost nothing.
I guess the question really would be, why not include it? If the waitvid function were there for VGA, which it would be right? Why not do NTSC? In fact, if it's there for VGA *at all*, then NTSC can be done, with the only real impact being the need to software generate chroma. The feature benefit significantly exceeds the very minor silicon cost.
It's quite baffling. Everything seems simpler than to use a TV. However, what potatohead said about video capture cards.. now that's interesting. If that could be used to connect some TV out, or at least S-video or composite to a laptop.. that would be convenient. Must look into that.
-Tor
Turns out women cannot live without TV so there has been one around for a long time. But then it is in the control of "Her indoors":)
Getting a small, cheap, TV just for hobby experiments is expensive. Small old TVs are impossible to find around here.
Currently, I have an outboard TV box that feeds into a VGA share with my old XP, but I have considered putting a card in the computer and many do come with video capture. I've just thought that it was better to conserve the electricity when watching TV by not having a computer on.
Thanks. This makes a lot of Propeller projects available with less clutter around the computer.
You can find this forum littered with captures I've done. My favorite mode is to run a 64 column display, color in my blog (80x50) for a resident text mode screen I can just output results to. I do a fair amount of business travel, and I take some prop stuff, the capture and a laptop or two, because my prop stuff is just nice to have setup on a older laptop.
The only downside I've run into is many of the viewer programs that come with capture devices introduce up to a second of latency. Often the "Preview" window in many movie authoring programs won't have it, or will have a fraction of that latency. So don't game on one.
When it comes to NTSC / PAL / Composite / S-video, capture cards are great! It's possible to sync your average laptop display to 50 / 60Hz, working reasonably with both standards. Ordinary definition capture cards perform reasonably well on a composite signal, and excellent on a s-video one. High definition capture cards (recommended) perform considerably better on composite, just FYI.
Re: Euro / American differences. I agree with those. The US has TV's all over the place. You can get them for nothing, and it's not hard. Big ones, little ones, extra ones, etc... And we fill them with absolute Smile most of the time too. Never did get it, but then again, I'm not your usual US fare, only watching a few hours per week tops. (Half that is on the Beeb anyway)
We even stuff TV's in our cars now, one of the primary reasons I drive older vehicles. Can't stand all the gadgets in the car! It's very common to see families with their kiddies plugged into something in the back seat, instead of actually experiencing the drive... I much prefer car talk and games. Deffo older school in that regard.
Growing up, I did TV repair in high-school for date money. Would do alignments too. Used my Atari for that, as it could generate most of the useful patterns and color references. Not a "pro" quality signal, but plenty good enough to align a TV for a great picture. Not so necessary today, but back then component aging really had a impact. A "factory fresh" look faded after, say 5 years. A readjustment usually brought that back, and I could get $20-50 a pop on those, angering the local TV guy, who wanted to see that "new fangled" computer thingy! A Prop does most of that today, minus the greys without some tricky programming, and can output a variety of signal variations as well! Damn cool. Interlaced, non, color phase change, non, full frame, overscan border, etc...
LOL@Heater: So true! Well, mine will also game with me, and at least "ooh" and "ahh" on the projects. I'm happy!