BECKHOFF EtherCAT Technology Section I - Manual (Page 22)

EtherCAT Slave Controller Overview
I-2 Slave Controller – Technology
1.1 EtherCAT Slave Controller Function Blocks
EtherCAT Interfaces (Ethernet/EBUS)
The EtherCAT interfaces or ports connect the ESC to other EtherCAT slaves and the master. The
MAC layer is integral part of the ESC. The physical layer may be Ethernet or EBUS. The physical
layer for EBUS is fully integrated into the ASICs. For Ethernet ports, external Ethernet PHYs connect
to the MII/RGMII/RMII ports of the ESC. Transmission speed for EtherCAT is fixed to 100 Mbit/s with
Full Duplex communication. Link state and communication status are reported to the Monitoring
device. EtherCAT slaves support 2-4 ports, the logical ports are numbered 0-1-2-3, formerly they were
denoted by A-B-C-D.
EtherCAT Processing Unit
The EtherCAT Processing Unit (EPU) receives, analyses, and processes the EtherCAT data stream. It
is logically located between port 0 and port 3. The main purpose of the EtherCAT Processing unit is to
enable and coordinate access to the internal registers and the memory space of the ESC, which can
be addressed both from the EtherCAT master and from the local application via the PDI. Data
exchange between master and slave application is comparable to a dual-ported memory (process
memory), enhanced by special functions e.g. for consistency checking (SyncManager) and data
mapping (FMMU). The EtherCAT Processing Units contains the main function blocks of EtherCAT
slaves besides Auto-Forwarding, Loop-back function, and PDI.
Auto-Forwarder
The Auto-Forwarder receives the Ethernet frames, performs frame checking and forwards it to the
Loop-back function. Time stamps of received frames are generated by the Auto-Forwarder.
Loop-back function
The Loop-back function forwards Ethernet frames to the next logical port if there is either no link at a
port, or if the port is not available, or if the loop is closed for that port. The Loop-back function of port 0
forwards the frames to the EtherCAT Processing Unit. The loop settings can be controlled by the
EtherCAT master.
FMMU
Fieldbus Memory Management Units are used for bitwise mapping of logical addresses to physical
addresses of the ESC.
SyncManager
SyncManagers are responsible for consistent data exchange and mailbox communication between
EtherCAT master and slaves. The communication direction can be configured for each SyncManager.
Read or write transactions may generate events for the EtherCAT master and an attached µController
respectively. The SyncManagers are responsible for the main difference between and ESC and a
dual-ported memory, because they map addresses to different buffers and block accesses depending
on the SyncManager state. This is also a fundamental reason for bandwidth restrictions of the PDI.
Monitoring
The Monitoring unit contains error counters and watchdogs. The watchdogs are used for observing
communication and returning to a safe state in case of an error. Error counters are used for error
detection and analysis.
Reset
The integrated reset controller observes the supply voltage and controls external and internal resets
(ET1100 and ET1200 ASICs only).
PHY Management
The PHY Management unit communicates with Ethernet PHYs via the MII management interface. This
is either used by the master or by the slave. The MII management interface is used by the ESC itself
for optionally restarting auto negotiation after receive errors with the enhanced link detection
mechanism, and for the optional MI link detection and configuration feature.
Distributed Clock
Distributed Clocks (DC) allow for precisely synchronized generation of output signals and input
sampling, as well as time stamp generation of events. The synchronization may span the entire
EtherCAT network.