My first attempt at disassembly to work out what it was up to. Made a good guess at where the on-board UART is, and possibly the STEbus floppy and SCSI boards.
MC Magazine's article about a 68020 computer designed by R.D. Klein. It is in German but Google can translate it for you. Not STEbus but explains a lot about the 68020 operation and has example PAL equations too.