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HP Forum Archive 01

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Receiving infrared on a pc from 42s
Message #1 Posted by Rob Hunter on 18 Mar 1999, 9:46 a.m.

Hi all,

I have a 42S and was wondering if it is possible to receive infrared transmissions via the infrared port of my laptop and capture it in a terminal emulator. The character set is ASCII ish?? 0x41 = "A" for instance. Does anybody know the bit rate/parity settings etc. ?



Re: Receiving infrared on a PC from a 42s
Message #2 Posted by Andrés C. Rodríguez on 19 Mar 1999, 6:41 a.m.,
in response to message #1 by Rob Hunter

The PCs use a standard called IRDA (Infrared Data Access, I think), which is very similar to a standard (asynchronous)serial link. That is why IRDA is usually set as an optional COM: port, up to 115 bps. There is a newer version of IRDA, that works on the same principles, but reaching megabit rates. The -42S is an early machine, from the IR point of view, and uses a proprietary (non standard) protocol to communicate with the printer. So there is no code compatibility (not true ASCII); but, even more important, the character "frame", the checksums, and so on are not standard. Simply stated, there were no such standard at the time the -42 was introduced. I even doubt that the pulse modulation over the IR components is the same than the one used in IRDA. So, there are many incompatibility issues; and since I don't think the PC will allow software to "see" the IR hardware at its lowest level, such a project may be very difficult. I don't know of any commercial or shareware product that may be of interest. I may assume that hooking a phototransistor on a convenient signal pin on a serial or paralell port may be a good point to start. Some assembler programming will surely be needed. If the PC processor is to service this input, it will be difficult to assure that no pulses will be lost. The PC is an interrupt driven system, and even more complicated since Windows virtualizes the hardware devices, so it is very possible to lose pulses. On the other hand, if you start planning a specific hardware that supports this interface, costs will raise... Well, this is a brief account on why I abandoned my IR experiments between a -42S and a computer some years ago. Certainly, anyone that goes further deserve a congratulation, so please keep us updated !

Re: Receiving infrared on a PC from a 42s
Message #3 Posted by Mike on 19 Mar 1999, 12:03 p.m.,
in response to message #2 by Andrés C. Rodríguez

The only way I know is via a HP-48

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