I have other issues with this. If that board really just has the components you say and *doesn't* have some sort of microcontroller on it then I can't in the slightest wrap my head around why it has a ROM chip on it. (Part of a state machine that initializes the serial chip into a hardcoded transfer mode without needed a CPU?) How fat of a connector this to the main board? (Seriously, there don't seem to be *any* pictures of the guts of these things online.)
28 pin interface back to the logic board. I don't know how the pins are used or even if they are all used. 28 pins for the external floppy, which uses essentially the same interface board. 44 pins or some such on the internal connector. Whatever an IDE hard drive + power connectors would use.
Also, that 28 pin external cable/interface is used both for the external floppy and the external SCSI adapter (one or the other). Both boards have an 85C30 at the input end, facing that 28 pin connector. The SCSI adapter pretty much just has a 53C80, and a GAL in addition to the 85C30. I can't remember if it also has a flash. I should check my notes at home.
I've always assumed that the ROM is there as a simple logic translation device. If I have an input of 12 give me an output of 4F. That kind of thing. Again, would need to create a schematic for more information.
Yep, no pictures on line that I've ever seen. Next time I did one out I'll take some photos. I wish I still had a scanner. Scans of circuit boards on a flatbed have always turned out better than my photography efforts, even when I remember to put the camera in Macro mode.