ControlNet - Data transfers

ControlNet supports both scheduled and unscheduled transfers.

Scheduled Transfer

Time critical data is scheduled data and deterministic and repeatable transfers that are continuous and asynchronous to the ladder logic program scan are called Scheduled data transfers. It occurs at a consistent rate that is either at the same or faster than the rate specified in an I/O map-table entry.

Unscheduled Transfer

Non-time critical data is unscheduled data and non-deterministic data transfers through ladder-initiated communication or programming devices are known as unscheduled transfers.A ControlNet network allows unscheduled messaging when deterministic delivery is not required. Unscheduled operations include unscheduled non-discrete I/O data transfers through ControlNet I/O Transfer instructions (CIOs)in the PLC ladder program and peer-to-peer messaging through Message instructions (MSGs) in the PLC ladder program. Unscheduled transfers are performed during the unscheduled time in the network update interval.  Number of nodes,application program, Network Update Time(NUT), etc. help determine how much time there is for unscheduled messaging.

Network Update Time (NUT)

It is the repetitive time interval in which data can be transmitted over the ControlNet network. Data cannot transfer faster than NUT.