Gerald Q. Maguire Jr.'s notes on using the HP iPAQ h5550

Hewlett-Packard Company (HP) iPAQ Pocket PC h5550: Specifications

iPAQ Pocket PC h5550 with stylus

  1. Intel® 400 MHz processor with XScale technology (PXA255)
  2. 128 MB SDRAM, 48 MB Flash ROM (of which 17MB is available as a File Store -- i.e., retained despite full resets; use the iPAQ Backup utility to copy files from the RAM file system to this area)
  3. integrated Bluetooth® v1.1 (using National Semiconductor's LMX9814 Bluetooth™ WPAN Module) and WLAN 802.11b (aka Wi-Fi based on Atmel's USB 11-megabit WLAN Media Access Controller chip AT76C503A (built around a ARM7TDMI core) and a front end RF chip from RF Micro Devices; note the MAC address 00:02:8A:xx:xx:xx is assigned to Ambit Microsystems (now Hon Hai's Network Systems Group (NSG))
  4. biometric fingerprint reader - based on thermal imaging using Atmel's AT77C101B FingerChip™
  5. Secure Digital Card slot: Secure Digital (SD), Secure Digital Input/Output (SDIO), and MultiMedia Cards (MMC) support
  6. Transflective TFT LCD display, 16-bit, 240 x 320 resolution, 3.8" diagonal viewable image size
  7. overlay for pen and touch interface
  8. audio microphone, speaker, one 3.5 mm stereo headphone jack; driven by an Asahi Kasei AK4535 16 bit stereo CODEC with headphone/speaker/microphone amplifier
  9. USB/Serial connectivity
  10. photosensor for authomatic backlight adjustment
  11. vibrating alarm
  12. 1250 mAh lithium polymer battery
  13. size: 13.8 x 83.8 x 16 mm
  14. weight: ~200g
  15. case secure by four Torx size 6 screws
  16. Built by High Tech Computer (HTC) - producer (original design manufacturer) of Pocket PC-based PDAs

The preinstalled OS is Microsoft® Pocket PC 2003. This OS also seems to be called "Windows® Mobile 2003". Examples of using this software - with lots of screen shots.

Additionally each user has an iPAQ PC Card Expansion Pack Plus - which enables them to add a PC Card to the iPAQ. This sleeve can accommodate a PC Card type II card slot. The "Plus" aspect refers to the hinged clear smoked plastic screen cover and a removable 920 mAh "Slim" battery.

Secure Digital vs. MultiMedia Cards (MMC) support

SD cards feature a write-protect switch and have support for securing data via "Content Protection for Recordable Media (CPRM)". This copyright protection technology was developed by 4C (IBM®, Intel®, Matsushita®, and Toshiba®).


The stereo microphone and headphone jack in the iPAQ is 3.5mm. To use headsets with 2.5mm connector you need to use an adapter (such as the Plantronics Adapter for HP iPAQ Pocket PCs). Note that this is actually a combo headphone/mic jack, hence it uses a 4-position 3.5 mm connector. [Vincenzo Ragone reports that the same cable will also work on an Axim x50v.]

One can easily make an adaptor for a soundcard compatible headphone/microphone.


The AC power adaptor is a 5VDC 2000mA center pin positive polarity supply.

The DC plug adapter allows you to connect the AC power adaptor directly to the iPAQ (i.e., without using the cradle). This adaptor is useful when you want to charge the iPAQ and it is failing to charge when in the cradle.

PC Card Expansion sleeve - useful for using PC Card (for example a wired Ethernet - I have successfully used the sohoware™ Ethernet 16 bit PC card)

Cradle - provides both USB and serial connections. You should not connect both serial and USB connections at the same time. A view of the iPAQ in the cradle.

Bottom view of iPAQ showing connectors, audio jack, and reset switch
Bottom view of iPAQ showing connectors, audio jack, and reset switch

Pinout of 22pin connector from Gomadic's support page.
V_ADP = AC adapter power in, TXD is tranmitted data from the iPAQ
1V_ADP6DCD RS23211DSR RS23216No Connect
2V_ADP7RXD RS23212RTS RS23217USB Detect
3V_ADP8TXD RS23213CTS RS23218No Connect20No Connect
4V_ADP9DTR RS23214RI RS23219USB: UDC +21USB: UDC -
5Reserved10GND 15GND22GND

If you are thinking of developing simple accessories, etc. Gomadic sells prewired cables, connectors, etc.

If you are thinking about making things which connect to this bottom connector, see the excellent web page " Compaq iPAQ USB Cradle Charger Modification" by Charlie Reverte, January 27th, 2002. This page has a nice closeup picture of what the board in the iPAQ cradle looks like. See also a similar article about modifying an iPAQ 3870 cradle.

Leather cover for iPAQ. iPAQ in such a cover.
There are also other types of covers available (but we don't have them).

Common functions

To access files from a samba server via the Internet Explorer, enter:


You should see (e.g., using ethereal) this hostname being broadcast using NetBIOS datagram service, server message block protocol, Mailslot protocol, Microsoft Windows® Browser Protocol in the field Host Name.

If you have several trees exported from this file server you might be able to enter:


If you are successful accessing the samba server, you will be prompted for you user name and password.

VNC client or server

It is offen useful to use the iPAQ to view a remote desktop (i.e. as a vnc client) or to allow a remote vnc client to view the iPAQ (i.e., a vnc server).

Another remote control package is Microsoft's Remote Display Control for Pocket PC ( current link as of 20080228) or SnapFiles' link to Remote Display Control


Other software (source)

Powering on the iPAQ


Desired actionSolution
Switch on Pocket PC at given time Set the Alarm Clock to go off at a certain time
Use CeRunAppAtTime with a special application that does nothing
Run an application when the Pocket PC is switched on (using the power button) Use CeRunAppAtEvent with an event of NOTIFICATION_EVENT_WAKEUP
Run an application when the Pocket PC is reset (that is, a warm reset) Place a link to your application into the \Windows\Startup directory
Run an application at a given time, regardless of whether the Pocket PC is switched on or off Use CeRunAppAtTime

Commercial software

Linux has ported linux to the iPAQ and some people at KTH has run this software. Including minisip. Before you put linux on, be sure to save the bits of the original ROM - so that you can put them back before you return your iPAQ.

SynCE is an open source synchronization solution between Linux Desktops and Windows® CE clients

Some notes from Alan W Black (author of the Festival speech synthesis program) about running programs on a WinCE device when you don't have a Windows® system to connect it to



Navman's GPS 3450 iPAQ sleeve or Navman's GPS 4400 Wireless - Bluetooth-enabled GPS device. See also Pocket GPS Portable Navigator in CompactFlash format and Pharos Bluetooth Pocket GPS Navigator

Reviews and other sources of information

Li Wei's iPAQ Tutorial for KTH/DSV students.

Alisa Devlic has produced a set of instructions on how to develop GPS applications in .NET Compact Framework and deploy them on IPAQ. She has used Franson GpsTools.

AdamaDBrown's iPaq 5550 and iPaq 5555 Review(8/24/2003) and Lisa Gade's HP iPAQ 5550 Pocket PC 2003 with 400 MHz XScale Processor, posted Sept. 7th, 2003.

Pravir Chawdhry send some notes on 2005.11.29

Toshiba makes several PC Card Hard Drives: 2 and 5 gig PCMCIA card drives; which could be used in the PC Card Expansion Pack.

Virus/Worm/... attacks

The first Trojan horse has appeared: Backdoor.WinCE.Brador.a is a utility which installs it self as SVCHOST.EXE in the following folder:

      <Root folder>\Windows\Startup

Thus it is automatic executed at every system startup. A description of its behavior, messages, ports used, etc. is detailed available - see also.

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Latest update 10 November 2008, small fix 22 January 2015
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