> I also wonder why use NTSC for outputting video. VGA is easy enough to bitbang and pretty ubiquitous. HDMI is probably more available at this point, but has unfriendly licensing issues. DisplayPort seems better in all aspects, but it’s the least user friendly and requires a monitor rather than a small TV.
Period authenticity, color palette, and pin count, among other reasons:
The idea was to make something that really felt like an old 8-bit you could build, and composite video output was a big part of that.
The NTSC colors were also a lot closer to the "feel" I wanted the computer to have, and unlike VGA output on the Propeller, you don't have to increase the number of pins to increase the number of output colors; the color information is conveyed by the phase of the NTSC signal. On the Propeller you can get a rather large NTSC (or PAL) palette with a 3-pin DAC, but with VGA, you'd want a six-pin DAC plus H and V signals for VGA (and likely not find color matches as close to the C64 palette anyway).
You also need to take into account the timing limitations for "racing the beam" and generating the video on the fly as the Propeller firmware is doing internally; TV scan rates are comparatively slow and give you more time to assemble a line of pixels.
Lastly, as far as HDMI or DisplayPort, that was well out of scope for what I was trying to do, and likely out of range of what the Propeller could bit-bang even with its shift register hardware. I know people have done something similar with DVI output from the Pi Pico, but I'm still not sure that even the Pico could do as much as the Propeller is doing here overall, and probably not as cleanly.
One of the things about engineering, or really anything, is that's more often than not a matter of finding the least bad option given competing constraints; in this case what I thought was the best technical fit was also the one that fit the 1980s aesthetic.
I did some cursory reading on Propeller and Propeller 2 and they seem really geared towards TV timings, and the perfect choice for a 200x320 screen with composite output. One of the reasons I mentioned DisplayPort is that, AFAIK, you don't need to race an imaginary beam with it.
> fit the 1980s aesthetic.
Can't blame you for that - the 80's is where I grew up and that feel is unbeatable (even though I liked the higher-end gear from DEC and IBM as well).
Period authenticity, color palette, and pin count, among other reasons:
The idea was to make something that really felt like an old 8-bit you could build, and composite video output was a big part of that.
The NTSC colors were also a lot closer to the "feel" I wanted the computer to have, and unlike VGA output on the Propeller, you don't have to increase the number of pins to increase the number of output colors; the color information is conveyed by the phase of the NTSC signal. On the Propeller you can get a rather large NTSC (or PAL) palette with a 3-pin DAC, but with VGA, you'd want a six-pin DAC plus H and V signals for VGA (and likely not find color matches as close to the C64 palette anyway).
You also need to take into account the timing limitations for "racing the beam" and generating the video on the fly as the Propeller firmware is doing internally; TV scan rates are comparatively slow and give you more time to assemble a line of pixels.
Lastly, as far as HDMI or DisplayPort, that was well out of scope for what I was trying to do, and likely out of range of what the Propeller could bit-bang even with its shift register hardware. I know people have done something similar with DVI output from the Pi Pico, but I'm still not sure that even the Pico could do as much as the Propeller is doing here overall, and probably not as cleanly.
One of the things about engineering, or really anything, is that's more often than not a matter of finding the least bad option given competing constraints; in this case what I thought was the best technical fit was also the one that fit the 1980s aesthetic.