1. An apparatus, comprising: a plurality of input/output (“I/O”) ports; measurement circuitry to measure one or more electrical properties of one or more devices to be externally coupled to one or more of the I/O ports; and a I/O multiplexer bus coupled between the I/O ports and the measurement circuitry, the I/O multiplexer bus programmable to selectively couple the measurement circuitry to any of the I/O ports, wherein the I/O multiplexer bus includes; a bus line coupled to the measurement circuitry; a plurality of bus line switches, each coupled between one of the I/O ports and the bus line; and switching logic coupled to the bus line switches to control the bus line switches; and a current source coupled to the bus line to drive a current through the bus line, wherein the switching logic is coupled to selectively drive the current through one or more of the I/O ports.