So, people, this got me thinking. Sorry if this is entirely the wrong place for this post. If so, any pointers welcome.

Anyhow, since it apparently is so easy (hardware wise, anyway) to make a VGA666 GPIO output from the Raspberry, can this approach be tweaked to do:


15 kHz RGB output? This way, Raspberry Pi could drive arcade and TV monitors for faithful emulation of old video games but with greater color separation than you get from the built in composite output.

2) SVIDEO output. https://en.wikipedia.org/wiki/S-Video

3) Composite video. At first glance, this may seem pointless, but AFAIK the built in composite output can not do progressive PAL/NTSC output, just interlace. https://en.wikipedia.org/wiki/Composite_video

4) Drive the deflectors on an old black and white monitor/TV (X & Y) and video intensity directly? (OK - this is pretty far out.)

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    Why not just use the composite video output on the Pi? – Milliways Oct 4 '16 at 23:45
  • The composite output cannot, as far as I know, not output anything but interlace, like 480i. It can't output what is informally known as PAL/NTSC 240p, which was very popular with 1980s computers and game consoles. @Milliways – Prof. Falken Oct 5 '16 at 7:13

Take a look at the Uzebox project, it has a circuit for doing exactly that, creating NTSC video from GPIOs (from an ATmega, but that doesn't matter at all.)

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  • Actually it matters a great deal. The GPIO pins of a raspi can not be programmed like that unless you are running without an OS on the bare metal. – Prof. Falken Oct 12 '16 at 15:10
  • Please see raspberrypi.org/blog/gert-vga-adapter. That's the same for VGA output. NTSC output only needs different (slower!) timing plus the DAC resistor network and the NTSC color coder chip used in the Uzebox. – Janka Oct 12 '16 at 16:11
  • Ok, I know about the gert-vga adapter. But how would you make it output at a slower timing? This is the holy grail but where is that timing specified? And by NTSC color coder chip, I assume you mean the AD725? – Prof. Falken Oct 13 '16 at 12:30
  • It uses the DPI parallel display interface the BCM283x has. Can be configured separately from the HDMI output, custom timings are done like this: raspberrypi.org/documentation/hardware/raspberrypi/dpi/…. And yes, the AD725 is the color coder. – Janka Oct 13 '16 at 22:57
  • Ok, I will look in to that. I did not know the Gert VGA could have its timings configured. If I can get it down to 15kHz I am done! (Plus an AD725). – Prof. Falken Oct 14 '16 at 13:11

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