IR printer data format (from 42 etc)


Does anyone know anything about the format of the IR data stream emitted by the HP42, eg data rate, coding, is text vs graphics etc



There's not much to know, but there's a good site for the printer (with a printer emulator for the 48). Maybe you can get some info from there.

Look at:

He describes printer codes, data rate ...



There was an HP Journal issue, about 1998, in which the IR pulses coding of the calculator-to-printer link was described. I recall a strange detail, the checksum was computed by means of a AND function, instead of the usual XOR (XOR is normally preferred because it maintains more information content than AND). If you read my "guest contribution" (here at this Museum), you'll see that I tried, in time, to made some kind of external hookup to my HP 25, and later to my 41C. While not included in that article, I had also tried to pick IR pulses from my HP 42S with a simple phototransistor circuit, and to so "upload" the pulses to a PC. Although part of the experiment worked, I was not able to pursue it much after the first trials (around 1991)...


The HP Journal issue was circa 1988, not 1998!


I did the same with a friend when I got my 48SX. The IR connection reached about 4 meters, but the filtering was not easy with my home-built IR circuit. The noise level was very high, if light was on. I wanted to do bi-directional IR comms, but this impossible with a HP calc without extensive external. I've never read the IR printer article, just looked up with an oscilloscope.

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