The output to the TV from the PIC microcontroller is a very simple circuit. For the audio, it is merely a 0.47uF capacitor, to avoid DC current bias. For the video, it is two resistors. The actual values should be 450 Ohm and 900 Ohm, but 1k Ohm and 470 Ohm are close enough, and work really well. These are used to generate the appropriate voltages (low threshold, black, white and gray). Gray could be used for two levels of output, but due to the speed limitations of the microcontroller this state is not used. Basically the 1k Ohm pin is used the generate the threshold voltages for syncing, and the 470 Ohm pin is used to generate the actual black and white values in the output. The circuit assumes the TV has an internal resistance of 50-75 Ohm, which is generally the case, to generate 0V, 0.4V and 1.2V levels.
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