During an online upgrade of CHARMs I/O, CHARMs maintain their outputs regardless of the configured Fail_Action_Mode (Hold last value or Go to configured failure action value). This is called a bumpless upgrade. When the upgrade completes, the CHARMs accept new output values and continue normally.
The exception is Discrete Output (DO ) CHARMs configured as Momentary Output or Continuous Pulse Output. For these CHARMs, the output is not bumpless during the online upgrade. When the upgrade completes, a DO CHARM configured as Momentary Output or Continuous Pulse Output accepts new output values and continues normally.