Asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Asynchronous literally means not synchronous, meaning, data is not transmitted at regular intervals, thus making possible variable bit rate, and that the transmitter and receiver clock generators do not have to be exactly synchronized all the time.
Deterministic communication is the transmission of data reaching its destination in a specific, predicable time. Time critical data transfer must be guaranteed within short and precise configurable cycles, while less critical data can be transmitted in asynchronous time slots. Data reaching its destination at guaranteed times are critical for motion control.
A deterministic bus based motion controller topology splits the motion controller functionality across a communication interface device and intelligent drive via a deterministic digital network. The communication interface device typically resides within a PLC or PC system and contains the trajectory generator. The intelligent drives typically contain the control loop and interpolator and can be daisy chained to other intelligent drives on the same network. The digital network is deterministic with low jitter to allow for tight coordination in multi axes applications. The benefits include all digital communication, detailed diagnostics, reduced cabling, high axes count, tight coordination, and short wiring distance between the drive and motor. This topology has a higher cost especially at lower axes count. Examples of this topology include EtherCAT, SERCOS, Ethernet Powerlink, PROFINET IRT, SynqNet, CANopen, and others.