[Coco] Coco Sound - Cartridge Input

[Michael Rowen]

   Hi Andrew,
   Yes, sound from carts comes over the SND line. The Game Master cart
   utilizes this. You can watch a video explaining the sound mux here:
   https://youtu.be/ikxREIHVk9k
   The Game Master cart utilizes the SND line with a SN76489 sound chip.
   There are 3 videos describing it in detail.
   Cheers,
   -Mike Rowen