Macintosh IIfx SCC
SCC Implementation on the Macintosh commonly is an 8350 IC connected through the VIA which is in turn connected through the processor lines. The Macintosh IIfx utilizes an IOP to directly control the SCC and handle all communication between the SCC and the main processor. As noted on page 362 of Guide to Macintosh Family Hardware access by the MC68030 directly to the SCC register space causes a bus error.
The IOPs use their own static memory area and do not share the main processor memory area. The registers on the IOPs can ba accessed by IOP DMA lines.
[Note: All block diagrams in the Guide to Macintosh Family Hardware detail the connections between the IOP and the appropriate device. Absolutely no connections are detailed between the IOP and the main processor .]
Below is a diagram of the SCC on the IIfx*. This is the only documentation that I could find on the SCC for the Macintosh IIfx. Click on the graphic to view a larger image.
* Information gathered from Guide to Macintosh Family Hardware.