Sync / Composite Video In (Scart Pin 20): The sync pulses are active low signals on the composite video line: 1.0 volts = White. 0.3 volts = Black, 0 volts = Sync ("blacker than black") So in RGB mode the line is normally 0.3v, pulsed to 0v for the sync periods.

Red (Scart Pin 15), Green (Scart Pin 11), Blue (Scart Pin 7) Inputs: 0.7 volts = peak intensity of colour, 0 volts = lowest intensity of colour. Note: I've found that my TV does weird things if there any voltages above zero present on the RGB lines during the sync / back porch periods (stuff like switching out of RGB scart mode, treating the colour present during sync as a black reference) so it seems its necessary to inhibit your RGB outputs during those times.

RGB mode select ("Blanking" Scart Pin 16): Some TV's let you toggle RGB mode via the remote but to force it, put 1 to 3 volts on this pin. (5 volts via a 100 Ohm resistor will set it at 2.1v due to the 75 Ohm load in the TV)

Note: All video (and control) signal lines see a 75 Ohm impedance at the TV end.

Video Ground: Scart pin 17.

Audio in (if required). Scart Pin 2 - left channel (or mono), Scart Pin 6 - right channel: 1 Volt peak-peak signals (about 20K Ohms impedance)

Audio Ground: Scart pin 4.

SCART CONNECTOR PINOUT Table 1

Table 1 was the original and allows for composite video input/output, RGB inputs and stereo audio. Table 2 was added to take S-video (S-VHS and Hi-8) inputs. This made pin 15 chrominance and pin 20 luminance. Many TV sets have 2 SCART sockets. One is usually loke table 1 and the other like table 2, and pin 20 switchable from composite to S-Video luminance. The first can switch from a composite input to RGB input. The second can switch from a composite input to an S-Video input, pin 20 being either composite in or luminance in. Usually the second socket outputs a selectable composite signal on pin 19.
Pin	Signal	Level	Impedance
1	Audio Out Right	0.5 V rms	<1k ohm
2	Audio In Right	0.5 V rms	>10k ohm
3	Audio Out Left + Mono	0.5 V rms	<1k ohm
4	Ground Audio
5	RGB Ground Blue
6	Audio In Left + Mono	0.5 V rms	>10k ohm
7	RGB Blue In	0.7 V	75 ohm
8	Audio/RGB switch / 16:9	High (9.5-12V) AVmode Low (0-2V) TVmode	>10kohm
9	RGB Ground Green
10	Comms Data 2
11	RGB Green In	0.7 V	75 ohm
12	Comms Data 1
13	RGB Ground Red
14	Ground Data
15	RGB Red In / Chrominance	0.7 V (Chrom.: 0.3 V burst)	75 ohm
16	Blanking Signal	High (1-3V) RGB Low (0-0.4V) Composite	75 ohm
17	Ground Composite Video
18	Ground Blanking Signal
19	Composite Video Out	1V including sync	75 ohm
20	Composite Video In	1V including sync	75 ohm
21	Ground/Shield (Chassis)

SCART CONNECTOR PINOUT Table 2

S-Video Connection Pinout
PIN	DESCRIPTION		Impedance	Level
1	GND	Ground (Y)
2	GND	Ground (C)
3	Y	Intensity (Luminance)	75 Ohms	1V incl. Sync.
4	C	Color (Chrominance)	75 Ohms	0.3V Burst
View to the solder side of the male connector