The HP ProLiant DL580 systems (G5 is the one I'm interested in at the moment) have a two-digit 7-segment display on the system board (visible only inside the chassis) which displays various diagnostic codes which they refer to as "port 84" or "port 85", switchable via a DIP switch.
The manuals mention this display but give only sketchy information about the actual codes displayed. Is there anywhere I could find a more specific & complete reference of the display codes? (I've done some web searches but have so far found only unrelated results.)
You should not need to reference port codes unless you're really having an issue with the server getting through the POST process.
What behavior is the server exhibiting?
The ProLiant POST boot troubleshooting flowchart still indicates checking the codes as a necessary step. It's not valid on newer boxes, but the ProLiant DL580 G5 you're dealing with uses them.
The full reference of Port 85 codes appears on page 64 of the HP ProLiant DL580 Generation 5 Server Maintenance and Service Guide. In general, the action needed to remediate the issues is reseating of the proper components.