RGB Formats
Various RGB video standards are used for many different video connectors.
In general, the red, green and blue information are all on their own individual wires, and the sync information is sent differently.
The key difference between many types of RGB is simply the way the synchronisation between frames happens by detecting the horizontal line and vertical frame pulses to know when lines and full image frames start.
The first and most common kind is to simply use a full composite video signal as the source of the sync signal.
Also know as CVBS Sync or Sync on Composite.
Composite video is also know as CVBS which stands for Composite Video Baseband Signal or Color, Video, Blanking and Sync.
This is the dirtiest way to lock on to a frame and can easily cause jitter or frame lock issues due to having both chroma and luma data on top of the sync pulse.
The voltage level is 1Vpp (2Vpp when not connected to receiver) and the sync part of the signal is 300mV (or 600mV when not connected to receiver).
A sync stripper circuit can be used to convert CSync over Composite into Composite Sync (CSync) which removes all the chroma and luma from the composite signal leaving only the clean sync. There are integrated IC chips such as the LM1881 that can do this.
Composite is made up of Luma (brightness), Chroma (color) and Sync. If you remove Luma and Chroma, you get pure sync.
This is then called CSync (composite sync) referring to just the sync portion of composite.
Using only the sync portion of the composite signal present you get a much cleaner pulse.
Sometimes people use the term Composite Sync to mean either Sync On Composite (including all of the composite video signal) or meaning CSync (just the sync portion), but technically CSync refers to just the sync portion of the composite signal.
For the sync portion of composite, a short pulses indicate new lines, and 3 long pulses indicate a new frame.
This type of sync is very clean and recommended as the cleanest way.
The voltage level is typically 300mV (or 600mV when not connected to receiver).
This is Csync just 5V instead of 0.6V signal level (2.5V when halved by receiver).
The next best thing after CSync if that isn't available is the S-Videos Y signal (which is the Sync and Luma signals of composite, without chroma).
This is passed into the same pin on SCART as the other sync pins (so pin 20 composite in on Euro Scart for example), and is cleaner than Sync Over Composite (full composite signal) but not as clean as CSync (just sync signal) as the Luma is still present.
Used most commonly in RGBHV which is the standard used for component video and VGA.
HV or Separate Sync refers to the sync signals being split into two separate signals, on two wires. One for horizontal pulses (lines) and one for vertical pulses (frames).
This is the most common form of RGB signal typically sent over SCART.
With RGBs, the most common connector is SCART. It uses the Red, Green and Blue pins of the SCART connector, as well as Composite In pin for the sync.
The sync pin on the SCART is typically CSync Over Composite, but depending on the receiver (such as a Framemeister, RetroTink or OSSC) you may want to pass in cleaner types of sync such as CSync.
This is the same as RGBcvS, but instead of CSync Over Composite it uses pure CSync as the sync.
Also known as Pass-Through Sync, this is identical to RGBs (CSync) but instead of 0.6V CSync it is 5V (2.5V once halved by receiver).
This is the same as RGBs (CSync) but instead of pure CSync as the sync signal, it uses Sync On Luma (so sync and luma information, which is the S-Video Y signal).
Unlike most RGB formats, Sync On Green doesn't use a separate wire for the sync signal.
Instead, the sync signal is Csync but sent over with the green signal.
Commonly used in video cables like VGA, RGBHV uses 5 signals (Red, Green and Blue, then both horizontal and vertical pulses).
Component video is often also referred to as RGB.
Although the cables are colored Red Green and Blue, they are not red green and blue information. They are YUV/YCbCr.
The signals in component are not the same as RGB signals such as RGBHV used in VGA, so you cannot switch between them the two using simple cable.
If you connect a component signal to an RGB monitor/TV, you’ll only get a green image. The R and B output will be very low.
Just like composite, the voltage levels of RGB and sync signals match the composite video standard.
Check out the Composite section for much more detail, but in short, Red Green and Blue lines should be 0.7V once terminated (connected to receiver) so 1.4V from 0 to 100% saturation when not terminated.
The sync voltage (unless TTL) should be 0.3V when terminated, or 0.6V when not terminated.
