As I remember the 8 Pin TTL digital connector is for CGA or EGA (Monochrome, 4 or 16 colors).
The other connector is Analog RGB which is what the Amiga uses. The 1084 is a versatile low frequency monitor and could be connected in a multiple of different ways to different computers. I think the C=128 could use the TTL connection in 80 column mode.
Jeff