Process Data Interface (PDI)

The Process Data Interface (PDI) is a critical hardware/software interface in EtherCAT Protocol Processors that manages the bidirectional transfer of process data between the EtherCAT master controller and slave devices. It handles cyclic data exchange for real-time control applications, including input data from sensors and output data to actuators, while ensuring deterministic communication timing and synchronization across the network.

Works as the local-side interface of an EtherCAT Slave Controller (ESC). While an EtherCAT frame passes through the slave, the ESC reads and writes the process data inside that frame on the fly, without stopping or storing the whole frame; those bytes land in the ESC internal dual-port memory. The PDI is the second port of that memory, through which the slave own application reaches the same locations. Depending on the PDI type selected in the ESC configuration registers, it presents itself either as a serial SPI port, as an 8- or 16-bit synchronous or asynchronous parallel bus for a local microcontroller, or, on slaves that carry no microcontroller at all, as up to 32 lines of direct digital I/O. Consistency between the network side and the application side is enforced by SyncManagers, which run a memory area either as a triple buffer for cyclic process data, so that each side always sees one complete image, or as a handshaked mailbox for acyclic data. Frame integrity is covered by the Ethernet CRC and by the working counter that every addressed slave increments as the frame passes.