@@curiouscomputer I am looking forward to new content. I also watched the second video (honestly, I watched the second video first because RU-vid suggested it to me :)
I think the only devices that ever used the HP-IB High Speed mode were the hard disk and the tape drives for the HP 9000 series. The most common HP-IB/GPIB devices like printers, plotters and data acquisition devices (e.g. HP rack multimeters etc) only used the regular modes.
What is the part number for the Mux board? 12040A, by any chance? If so, it's an 8-channel RS-232 serial card, based on a Z80 microprocessor. And, yes, the high speed HP-IB card was used to talk to the disks and tapes, at a massive (for the time) 1 megabyte / second.
@@curiouscomputer Ok, wow, that's a nice set of ports. The 12040A (and sister card 12792A for the M/E/F series) were line-oriented serial interfaces, best used for hooking terminals to the computers. I believe there was a firmware update at some point a few years after release that made them a bit better for random serial device interfacing, where strings didn't necessarily terminate in the carriage return character, though both versions would do either mode. The RTE drivers allowed adding a "device driver" to do higher level functions, such as managing the cartridge tape units on the 264x terminals. HP provided some, and the manual described how to write your own. The cards used a breakout cable and box with 8 of the 25-pin connectors, otherwise you're in for a lot of wiring. Hope they still work!
