When a new set of inputs reaches the system, it processes them, generates new outputs and updates its state.
This set of changes (new inputs, new outputs, new state) is considered to define that step, and must be treated as an atomic transaction; in other words, either all of it happens, or none of it happens, but not something in between.
Sometimes a timeshift (delay) is set between systems, which increases the detection probability of errors induced by external influences (e.g. voltage spikes, ionizing radiation, or in situ reverse engineering).
For this reason, it is common practice to run DMR systems as "master/slave" configurations with the slave as a "hot-standby" to the master, rather than in lockstep.
Should the master fail at some point, the slave is ready to continue from the previous known good step.