There are four types of clock triggering that determine when a sequential circuit responds to input changes: negative level triggering, positive level triggering, positive edge triggering, and negative edge triggering. Negative level triggering occurs when a flip flop is triggered at the negative/low level of the clock pulse. Positive level triggering occurs when a flip flop is triggered at the positive/high level of the clock pulse. Positive edge triggering occurs when the output responds to input changes only at the rising edge of the clock pulse. Negative edge triggering occurs when the output responds to input changes only at the falling edge of the clock pulse.
