A method and apparatus for allowing determination of patient position change relative to an imaging device andor allowing digital subtraction in an operative position. The ReRAM cells may include a first layer operable as a bottom electrode. The first busy write output signal indicates when the first memory controller releases the data bus for a next external access subsequent to a write access to the data bus by the first memory controller. The drive IC outputs an equalizing switch signal voltage to equalizing switches which connect the common electrode and data signal lines.