About the SCART Connector

The SCART connector was invented as a way to carry video, audio and control signals between two video devices. It's most commonly used to connect a video recorder or DVD player to a TV with a single cable. The SCART connector is standard on most European audio-visual equipment but is almost unknown in the USA. More Info: Wikipedia entry for SCART.


RGB versus Composite Video
The Apple IIGS can connect to a display using a composite video cable, but Apple only intended this to be used for connecting a monochrome monitor. For a colour display the RGB video output was normally used. RGB stands for red, green and blue. This refers to the way the video is sent as seperate colour signals. The SCART connector on a TV allows for one type of connection which is not generally found on non-SCART TVs, and that's an RGB video input.


Benefits for the Apple IIGS
There are two advantages to using an RGB video connection over composite:

better picture quality since there is no need to convert from RGB to composite video in the computer and back again in the TV
you can use any colour system TV (PAL, SECAM or NTSC) with your IIGS whereas the computer's composite video only outputs in the NTSC standard
While the picture quality will never be as good as can be achieved with a true computer monitor, I have found that on a cheap 48 cm (20") TV 80-column text is legible and this size screen is great for games.

The rest of this page has details on making a cable to connect an Apple IIGS to a SCART TV. If you would like one but don't want to make your own I also sell them.


Cable
To make an RGB to SCART cable you will need a length of shielded multiple-core cable, with at least six cores - preferably more for sound and extra grounds. The highest quality video cable uses 75-ohm coaxial cores for the RGB video, medium quality cable uses shielded twisted pairs for the video, and the cheapest cable just uses plain conductors with an overall shield.

I have made cables using expensive coaxial cable and cheap shielded cable, and in comparing them found no difference in the picture quality. This is probably because the cables are under two metres in length, and carrying fairly low frequency video signals compared to the bandwidth required for modern computer displays.


Connectors
For the Apple IIGS end of the cable you will need a 15-pin sub-miniature D plug, also known as a DA-15 male (don't buy a DE-15 plug, sometimes called HD15, as this is the high-density version with three rows of pins instead of two and is commonly used for VGA video connectors). For the TV end you will need a SCART plug.

Wiring
Wire the plugs together using the tables above. The red, green and blue video signals are connected directly. If you are using twisted-pair or coaxial cable you can match the RGB grounds together. Any extra conductors you have in the cable can be used to connect the rest of the grounds together, but all the pins marked ground will be connected together inside the TV anyway. The composite sync from the IIGS is fed into the SCART composite video input. The IIGS sound should be fed into both the left and right audio inputs unless you have a stereo decoder card in your IIGS in which case you could wire up a seperate stereo plug.

The function select pin should be connected to +12V so that when the IIGS is turned on the TV will automatically switch from the tuner to the external input. I connect it via a 1kΩ resistor to safeguard against accidentally shorting the +12V output. Note that some TVs don't support this control line and have to be manually switched to AV mode.

The RGB control needs between 1V and 3V to switch from composite video mode to RGB mode. Connect it to the +12V via a 270Ω resistor. This resistor combined with the 75Ω input drops the voltage to about 2.5V at the RGB control pin.

The cable shield should be connected to the metal surround of the SCART plug (the so-called pin 21) and to the metal surround of the IIGS video plug.


Plug Backshell
The back of the Apple IIGS has a plastic layer over the metal panel through which the video socket projects. Most D plug backshells grip the plug with a plastic lip which curls over the front. The problem is that most of these are too thick and will prevent the plug from fitting into the IIGS properly. You may have to shop around to find one that will fit, or else cut the projections off and glue the back shell on.


Apple IIGS Setup
When you use a IIGS with a TV you may need to change the video frame frequency to get a full sized or stable picture. To do so hold down the option key while you turn on or reboot the computer and you will be given a menu to set the video to 50 or 60 hertz. Normally you need to set it to the same frequency as the TV standard you use, i.e. 50 Hz for PAL or SECAM and 60 Hz for NTSC. Note that changing this will also reset all your control panel settings to the default values.

http://roger.geek.nz/apple2/scart.html

http://roger.geek.nz/scart.html