A pen apparatus with a pressure sensitive tip mechanism that internally generates pressure, tilt, and/or barrel rotation through the use of a multi-axis measurement scheme with simultaneous transmit, receive, and sensing driver capability operable in conjunction with a receiving system or in a relative stand-alone manner. Signaling schemes are provided for operating the pen apparatus to achieve improved function. Systems and methods are provided for operating a pen, and for operating a pen with a touch sensor system. Drive/receive circuitry and methods of driving and receiving sensor electrode signals are provided that allow digital I/0 pins to be used to interface with touch sensor electrodes. This circuitry may be operated in modes to sense various combinations of signals coupled within a pen, or from outside of a pen.