This paper describes a programmable high speed multi-level simultaneous bi-directional I/O. With programmable high speed differential current switching, the static current flow becomes dependent upon the number of bits in the outgoing data, from 0-bit to 2-bit. The pre-emphasis method was implemented to enhance the transmission speed. Simulation results based on 0.18micron CMOS process show the maximum data rate can be enhanced to 4.8-Gb/s/pin. Timing window and voltage window are 480ps and 43mV, respectively.