System for automatic identification of a computer data entry device interface type using a transistor to sense the voltage generated by the interface and output a matching voltage level

摘要

A circuit using a single transistor to detect the interface type to Which a combination pointing device is connected. The pointing device may be connected to a PS/2 interface, which generates a voltage greater than or equal to 0 volts, or a serial interface which generates a negative voltage. The transistor is activated when connected to the serial interface, and is inactive when connected to the PS/2 interface. The output of the transistor is sensed by a microcontroller within the pointing device. The microcontroller generates data for transmission to the PS/2 interface if the transistor is not active, and generates data for transmission to the serial interface if the transistor is active. An I/O pin in the microcontroller is used to sense the interface type and can also be used as an output in which the microcontroller generates control signals for use by the pointing device. This multitasking operation reduces the required pin count of the microcontroller, thus reducing cost.