A cardiac rhythm management system having a plurality of timers and programming adapted to receive a status array. The status array is based on the status of each timer of the plurality of timers and includes intrinsic activity detection for each pace sense site. The plurality of timers are initiated concurrent with a detected event or condition. The status array is masked according to an enable array and an interrupt signal is generated based on selected bit transitions of the status array. The interrupt signal initiates a predetermined therapy or function based on the status array. A FIFO buffer preserves the order of senses and paces for further processing. The predetermined therapy or function includes determining a mode of operation of the system.