A method for refreshing PCRAM cells programmed to a low resistance state and entire arrays of PCRAM cells uses a simple refresh scheme which does not require separate control and application of discrete refresh voltages to the PCRAM cells in an array. The theoretical radius of a pipe is computed from a measurement of its circumference. The method includes generating a plurality of output enable signals, which are utilized to respectively adjust a plurality of conduction durations of a plurality of gate lines of the corresponding regions. The encryption key is partitioned into a plurality of slices such that no slice comprises the whole encryption key. This DA converter in accordance with the invention may consist of a resistor ladder or a directly digitally controlled capacitor.