Medical infusion pump with power source voltage logging and method for logging a power source voltage in a medical infusion pump

A method for retrospectively determining a cause of a power supply interruption in a portable device, comprising:

• monitoring a processor supply voltage (VDD) via a voltage supervisor;
• responding if the processor supply voltage (VDD) drops to a predetermined response voltage level which is above a reset voltage level of the processor by providing an output signal via the voltage supervisor and logging a power source voltage (Vbat) in a memory to generate a voltage log, and maintaining in the memory logged data when the power supply by the power source is interrupted to enable retrospective analysis of the voltage log;
• and
• determining retrospectively the cause of the power supply interruption in the portable device by retrospectively analyzing the voltage log.