This signal is used to monitor the status of the configuration readback system (readback CRC) or any manual scanning of the configuration memory that is performed by the SEM controller. It is a direct output from the readback process and is active during the Observation, Detect only, and Diagnostic Scan states. After entering the Observation, Detect only, or Diagnostic Scan state, the heartbeat signal becomes active when the readback process is scanning for errors. The first heartbeat pulse observed during the Observation, Detect only, and Diagnostic Scan states must be used to arm any circuit that monitors for loss of heartbeat. In all other states, the heartbeat signal behavior is unspecified.