Battery operated computer having improved battery monitor and cell reversal protection circuit

DETAILED DESCRIPTION The following description is divided into sections that proceed from a more generalized description of the digitizer tablet computer, through a general description of service processor operations, and finally to specific descriptions of the battery monitor and cell reversal protection.
DIGITIZER TABLET COMPUTER Referring now to the drawings, and first to FIG.
1, reference numeral 10 denotes a digitizer tablet computer (DTC) that includes a casing 12 for housing the various components of the computer.
DTC 10 has a size and a weight that permit a user to readily carry computer 10 from place to place.
Housing or casing 12 may have an appearance such as that covered by the above-mentioned related design patent application.
DTC 10 includes a digitizer 14 mounted beneath a backlighted liquid crystal display (LCD) 16, and pen or stylus 18 that form the primary input/output means for entering information into and getting information out of the computer.
DTC 10 also includes means for connection to other I/O devices for use at locations where it is convenient to do so.
For example, an optional keyboard 20 may be used at a home or office location but not out in the field.
Computer 10 may also include system I/O (not shown) such as a SCSI diskette port, a parallel port, an RS 232 serial port, and a data/facsimile modem with an RJ11 connector.
Stylus 18 is the primary input device and is battery operated, cordless, inkless pen or stylus 18 which includes a movable tip that closes a switch (elements not shown) when brought into contact with the upper surface of the LCD.
Stylus 18 generates a magnetic field that is sensed or picked up by digitizer 14 and translated into signals representing X,Y coordinates indicative of pen position or location.
The field is weaker when the switch is open and stronger when the switch is closed so the digitizer can distinguish between "proximity" coordinates and "pen down" coordinates.
Computer 10 then operates the LCD, in a manner described in more detail hereinafter, to activate pixels close to the pen position so that the user perceives that he or she is actually writing with the pen