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Threads: 43
Joined: Jul 2005
The HP42S and other contemporary models (i.e.: 28C/S) use a proprietary protocol for their IR communications with the "Redeye" printers. It is not serial IR nor IRDA, which appeared many years later.
The protocol is described in the HP Journal issue where these models were discussed in some depth (1987).
Some years ago (you may look in the MoHPC Forum Archives) some people, including Steve (Australia) discussed how to receive those IR pulses with the audio input of a PC (at the time, via a Sound Blaster card).
I suppose that today some of the regulars here may like to develop a PIC or Atmel interface; say IR to USB/Serial... I suppose it could be done, but I'm far from hardware design in the last years...