I have the HPILCMDS lex file for the 75. It came to me on a copy of Swapdisk 12. I don't know if it started out there or not. The fellow who sent it to me said that among the Swapdisks, pretty much all the HP lex files were available. He also sent me the documentation for it (just a few pages) and the documentation (two pages) for, and a copy of, the 75 lex file RIOWIO, which he pointed out was on Swapdisk 2 or 3, one of the four original Swapdisks I had ordered from EduCalc years ago. I just looked on the Museum FTP site collection of separate LIF files and I've already forgotten exactly which Swapdisk but RIOWIO is there. RIOWIO provides low level access to the HPIL chip. It has one function - RIO(n) where n is the HPIL chip register (0 - 7), it returns the register contents as an integer from 0 - 255; and one statement - WIO n,x - where x is an integer from 0 to 255 to be written to register n. You'd have to know all about HPIL to get anywhere with those alone. The HPILCMDS (apparently that's not its official name: according to the documentation, it was provided on a 75 magnetic strip "card" and you are instructed to give it a name when you load it) lex file provides one instruction statement, SENDIO <device code>,<command list>,<data list> and one function, ENTIO$(<device code>,<command list>) which returns data received from the HPIL as a character string. These are high level programs that take care of all the HPIL overhead. You see examples of their use here and there, such as in the 9114B addendum that tells how to do a single sided format with different machines including the 75.
(I'm giving the Boy Scout salute now...) I promise to do my best to make LIF files from HPILCMDS and RIOWIO, and to scan the few pages of documentation, and to zip the files up in a convenient package. However, I can't promise exactly when I will be finished.