pen plotters?

I'm probably mis-remembering the numbers, but isn't the 98135 the HPIB interface for the 9815 calculator? I thought hte plotter had HPIB as standard. Nice! The old HP desktop calculators are not that easy to find (at least over here), and the interfaces/peripherals are consdierably rarer (makes sense, people bought/used the calculator on its own, but nobody bought the peipherals withput the calculator to drive them from). I don;t know how much you know about the 9815 internals, but anyway. It's a 6800-based design -- apart from the firmware ROMs, all the chips are stnadard :-). Therer are 2 itnerface slots on the back (well, that is technically an option, but as you have the interfaces, I assume your calculator has it fitted). Each slot can be logically divided into 2 sections. One is an input-only version of the 6800 bus (essentially common to both slots), the other is a 12 bit output port + control lines (separate for each slot). The interface modules cotnain firmware ROMs contining the driver software (in contrast to the 98x0 and other 98x5 machines, where the ROMs were seprate modules). Some of those ROMs have 'interesting' instructions, the BCD interface, for example, has an instruction to access the numaric storage registers at the byte level (letting you create non-normalised numbers, etc). I asusme you've found http://www.hpmuseum.net/ . There's a lot of info on the 9815 and interfaces there. I've come across that processor in the HP7245 thermal printer/plotter. For those who've not come across that machine, it's a plotter, but not a pen plotter. Basically, there's a thermal printhead with 13 elements. 12 of them aranged i na diagonal pattern, are used for printing dot matrix text -- the diagonal arangement is so that it can print acrros the paper or up and down the papepr equally easily. The 13th dot is used to draw lines like a pen plotter -- there's a complex motor control board to drive the 2 motors (hard movement and paper movement) jsut like in a pen plotter. It responds to 2 HPIB addresses. One of them is for printing, you send it ASCII characters and control condes. The other is for plotting, you send it HPGL commands. Yes, I have one, I undersand the electronics (even the 2-stage switching PSU), apart from the details of the processor.... I believe the same processor is used in the 9871 Daisywheel printer [1]. This is often claimed to be a Selectric mechanism, AFAIK it isn't (it's a daisywheel, pure and simple [2], but it does take Selectric ribbons, probably because they were easy to get at the time. [1] There's one listed on E-bay at the moment. Alas I can't afford the shipping to England.. ]2] Well, maybe 'simple' isn't the word for a machine with a toothed belt that follows a contorted path round sprockets on the chassis and carriage, and which is drivein by 2 motors such that one of them moves the carraigne, the other (also fixed oteh chassis and not the carriage) turns the daisywheel. I've not found out anyhting about it, nor any info on the eariler 80bit nanocontroler (1820-1691 or something similar) used in the 98x5 interface modules, the 9885 8" floppy drive, etc. -tony