TRS-80 Disk/Video Interface?

I was at one of the local thrift stores (a once a month or so experience) and found a Radio Shack TRS-80 Disk/Video Interface unit for $0.90 with manual. Apparently it was marked down from about $3.95 or so to get it gone and I was more than happy to help out at that price even not knowing what it was. After reading the manual, I still don't know but it talks about the portable computer and I see one reference to a model 100. Anyone have more information on this thing as far as what it attaches to? The model 100 is obvious but since it talks about the connecting it to the Portable Computer, are there others this thing might work with? Also since it didn't come with a floppy disk, is this just a standard TRS-DOS or is there something special about it? Finally, it is missing the connecting cable and does anyone have the pinout for it or know where I might find it on-line? Thanks!