Xerox PARCTAB Mobile Hardware

The PARCTAB mobile hardware (tab for short) is depicted in the picture above. Positioned over the display is a touch sensitive panel that can be operated coarsely with a finger or more accurately with a passive stylus. Both the touch panel and the display have a resolution of 128x64 pixels. The grip part of the tab incorporates three finger-operated mechanical buttons that can be used individually or in chords. Finally the unit includes a piezo-electric speaker that permits a number of different tones to be generated by applications.

The tab communicates using infrared signals at a speed of 19.2k baud. The spread of infrared emissions are contained by the walls of a room providing room-sized communication cells. The small cell size provides good aggregate bandwidth as long as few active units are in each cell. The room-sized cells employed by the communication network also generate location information used by higher level software.

Power management was an important consideration. For a compact and low power design we built the unit around a 12MHz Intel 8051 family 8-bit microcontroller with on-board EPROM, RAM and I/O ports. The tab can operate under nominal use for 10 minutes per hour, 8 hours per working day for about a week before needing to be recharged.

To foster casual use our design also paid special attention to ergonomic factors. The PARCTAB is designed into a custom, production-quality, plastic case with a removable belt clip, and is about half the size of current commercial PDAs. The package is symmetric and can be used in either hand. When converting from left to right hand use, a setup command rotates the display and touch-screen coordinates by 180 degrees.

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