Archived 2013-12-08
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Ways and problems of connecting the palmtop to differend kinds of devices via Infrared

Contents of this page:


I removed my instructions to build an IR transceiver device for Desktop PCs from this site, because there are now many other instructions available on the web which are way better than mine was. Another reason is that I used an Infrared transceiver component which is not available anymore, the HP HSDL 1001. The newer Vishay TDFS 4500 and similar products are a better choice nowadays.

You can find instructions to make infrared transceivers for your desktop PC here:

Please note that these transceivers connect directly to the "Infrared" connector on your motherboard. No way to connect them to a serial port or USB. For that purpose there are special devices called "IrDA dongles" available. You can buy these devices in several variations, the most common one nowadays may be the USB version.

Introduction: About IR communication with the HP DOS palmtops

The main issue with the palmtops HP 95LX, 100LX, 200LX, 1000CX and 700LX is, that these devices are not fully IrDA compliant.
IrDA defines several network layers. The lowest layer, the physical one, is SIR, also known as HPSIR, because HP invented it. This layer is supported by the HP LX palmtops, i.e. all IrDA devices arephysically able to establish an Infrared communication path to the palmtop.

But the logical way of communications causes problems: Almost all IrDA compliant devices which are available these days (e.g. cell phones, PDAs, Laptops, LAN adapters, digital cameras...) make use of some of the other layers defined by IrDA. These other layers are all implemented in software, so theycan be switched off if the software is modifyable, e.g. on laptops which run Linux. Maybe even IrDA drivers in Windows 9x can be made work in plain SIR mode by modifying the Windows registry (see PC part of this page below).

SIR (serial Infrared) is basically the RS232 protocol, but with other signal levels and impulse lenghts. All other IrDA protocol layers (IrLAP, IrLMP, IrCOMM, IrLAN, IrOBEX) are connection management and handling stuff, such as adjusting the baud rate, recognizing the peer device, setting up "virtual" ports which can be used by software which wants to talk to "normal" ports like LPT or COM or network devices and so on. As soon as software relies on these upper IrDA layers, a communication with the HP palmtop as is is impossible.

Why do I say "as is"? Read on!

Connecting to cellular phones

Well, there are exactly two programs by now which are able to drive the palmtop´s IR port in a more IrDA-compliant mode. Only a few parts of the full IrDA protocol are implemented there, so it is not possible to do all IrDA things with that software.

Both programs are written by Andreas Garzotto, one of them is commercial software and sold by D&A Software. It is called "WWW/LX". This is an Internet suite with TCP/IP stack, mail client, web browser, and clients for various purposes, such as FTP, finger, get, ping etc. This one supports talking to IrDA cell phones via IR, so you can use a cell phone as a modem or you can use AT commands in terminal mode or even automated to administrate your cell phone (phone book up/download, ring tones, logos etc.) WWW/LX implements parts of the IrCOMM, IrLAP and IrLMP protocols.

The other one is free software called "IR.EXE". This one implements the connection free part of the IrOBEX protocol in addition to IrLAP. IR.EXE is also available over the D&A software FTP server. You can send and receive OBEX objects with this software, which is also supported by cell phones, PDAs and other devices.

So if you want to connect to cell phones via IrDA, there is generally no big problem. Dependent on your needs you have up to two choices.

Regarding the specifications of different tested cell phones, please read my "mobile HPLX" page!

Connecting to other PCs for file transfer

If your computer and OS (or IR dongle device drivers) are capable to talk the plain SIR (serial Infrared) protocol via its IR port, everything is fine. Then you can use every application which you also would use with a serial cable connection to transfer files (Transfile Win200, Laplink Remote Access, zip, InterLink/InterServer, X-Finder....).

If your computer can "only" talk the full-featured IrDA protocol, you may have a problem. If you connect an IrDA transmitter device to your computer, Windows 98 recognizes it and sets up "virtual" COM and LPT ports. These port types are defined by the IrDA standard (IrCOMM), but are not suitable to communicate to the palmtop, because they use these advanced IrDA features (keywords IrCOMM, IrLTP, IrLMP, IrLAP etc. - I don´t want to go into detail here, please refer to The problem is that these "virtual" ports don´t use the plain (HP)SIR protocol, but all these add-on connection handling protocols, which the palmtop isn´t capable to handle. The above mentioned programs WWW/LX and IR.EXE are limited for use with cell phones and IrDA modems.

On the other side, you may need these IrDA-specific features on your PC if you want to use it to talk to a mobile phone, a newer PDA or some other real IrDA device.

What about a general IrDA driver for the palmtop?

This is an idea which has been mentioned a lot of times in the HPLX mailing list. But unfortunately, it is simply not possible to create a driver which sits between the application and the IR port, because the IR port is directly addressed by all DOS programs with their read / write routines. They speak directly to the hardware. So no other program or driver would have a chance to modify the data stream in any way before it is written to the serial port.

Do you like to support me?

Dear fellow Palmtopper!

If you like, you may reward me for the work I put into this website with a donation.


For a donation in US$:

For a donation in €:

Your donation, even if it's just a single USD, will help me to:

  • finance the server that hosts the site
  • justify time I spend with maintaining the site and do not spend with earning money otherwise (wife is watching! ;D)
  • just continue to be motivated :)

Since my company "hermocom" does not exist for many years anymore, I am now spending my spare time and private money for all of this. Thank you very much! 🙂

Yours truly,
Daniel Hertrich