Apple Technical Note HW 9 Macintosh IIfx The Inside Story
Download it here: Apple Technical Note HW 9 Macintosh IIfx The Inside Story.pdf
This is Apple Computer's own developer documentation for Macintosh IIfx, published in 1990. It covers why software that talks to Macintosh hardware directly breaks on the IIfx: the two I/O processors that take over the SWIM floppy controller, the ADB and the SCC; the IOP Bypass mode and the IIfx Serial Switch control panel; the missing VIA1 Wait/Request and vSync bits and the _HWPriv replacement; the NuBus read-modify-write erratum; and the fact that all of VIA2's functions have moved elsewhere.
Apple's developer notes are a different document from the Service Source repair manuals: the Service Source tells a technician which module to swap, while the developer note gives the electrical and architectural detail — rail currents, connector pinouts, power budgets and chip functions — that a repairer needs in order to make a go/no-go measurement. Several figures on this wiki are cited to this document.