This site has a nice and complete page about the HP-75C/D. You can even order the original manual.
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Otto (Brazil)
Monday 14th February 2011
I has one (serial $ 78). There was 2 lines on screen.
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Rodolfo Gil (Venezuela)
Friday 11th March 2005
Hi!. I´m found a HP75C in a trash can!. I´m want to bring it to life again. Do someboy have got an electronic version of its manual?. I will apreciate very much!. rodolfo.gil@uny.edu.ve / rufogil@hotmail.com
The HP-75C was the first pocket computer ever produced by HP who wanted a pocket book format (10”x 5”) computer as powerful as a desktop. It can also be considered as the first organizer able to deal with a multiple alarms time schedule, to control real time peripherals and to memorize text files.
Its 48KB ROM contained a very complete Basic language and a light version of the spreadsheet Visicalc. Three slots allowed adding pre-programmed ROM modules (Maths, finance, word processor…)
It integrated a card reader. The cards was manually slipped front of the magnetic head. Each card could stock 1.3 KB of information on 2 tracks (650 bytes each). The card information coding allowed great variations of the reading speed, due to manual handling.
The HP-IL (Interface Loop) interface allowed connecting as far as 30 peripherals simultaneously on the HP-75C. Amid the peripherals, one could find a display unit, printers, a modem, a tape recorder and all the HP-IL standard peripherals.
As always with HP, the manuals were very complete and pedagogical.
The HP-75D was released two years later. It added a wand and wand port. When used with the Bar Code ROM, the computer could scan CODE11, CODE39, UPC, and EAN codes. This made the computer useful for inventory control.