and 19 and resistors 11 connected between a source of voltage explained below and each of the output terminals of the encoders 13 and 15 and the switches 17 19 although two switches are shown the number of switches provided is arbitrary but generally is a relatively small number to simplify operation of the mouse the output terminals from each of the encoders 13 15 and switches 17 19 are connected to i o ports pa0 to pa5 respectively of a microcomputer 21 the encoders and switches are also connected to a local ground as explained below this local ground is different from the host computer ground at least the encoders 13 15 and the switches 17 19 will be located in the mouse enclosure all or part of the remaining circuitry can be located within the mouse enclosure or at the host computer connected to the mouse by a cable the encoders 13 15 are standard shaft encoders of a type that can be purchased from alps electric or from other sources microcomputer 21 is preferably an 8 bit cmos motorola mc 146805f2 as described in motorola publication adi 879 copyright 1982 by motorola inc the microcomputer is configured as specified in the above publication with the rom of the microcomputer being configured according to the source code of.