Multilevel timestamp detection circuit and method

Disclosed are methods and circuits for detecting and recording timestamps for multiple events (222/322, 224/324) using a single input pin (252, 352) on a real time clock (RTC) (250, 350). Signals associated with each of the events are modulated to create a multiple level composite signal (240). The RTC includes a multiple signal level detection circuit to distinguish from among the various signal levels so that each event can be separately flagged and timestamped. For example, the opening of two or more covers (112, 114) on the housing (110) of an electronic device (100) can be monitored, distinguished, and separately flagged using a single RTC input port.