Signetics 8x300 instruction set

I've been trying to recall, with no success, how subroutine calls were implemented in the 8x300. I used to write code for this weird thing (realtime video processing) and the assembler I used (some horror that ran under TSO) hid it from me so I don't have a clear recollection of the method. It's a really weird CPU, "subroutines" were essentially jumps, as in a lot of machines, but the "return" was through some strange jump table or something. Once upon a time there was a website with CPU instruction cards (man I had a huge pile of these things, pitched loooong ago...) but I can't find it. Nothing on bitsavers I can find. (There's also some really bad info out there on the origins of "Harvard" architecture, attributed to some stupid hardvard vs. princeton microprocessor design thing. Please -- about 40 years earlier: that asshole Aiken. No one liked him anyways.)