13.5 Synchronization with Distributed Clocks
13-8
13.5
Synchronization with Distributed Clocks
The synchronization of EtherCAT communications is based on a mechanism called a distrib-
uted clock. With the distributed clock, all devices are synchronized with each other by sharing
the same reference clock. The slave devices synchronize the internal applications to the Sync0
events that are generated according to the reference clock.
You can use the following synchronization modes with EtherCAT (CoE). You can change the
synchronization mode in the Sync Control registers (ESC registers 0x980 and 0x981).
•
Free-Run (ESC register 0x980 = 0x0000)
In Free-Run mode, the local cycle is independent from the communications cycle and master
cycle.
•
DC Mode (ESC register 0x980 = 0x0300)
In this mode, the SERVOPACK is synchronized with the host controller (master) on the Sync0
event.
The following figure gives a timing chart for DC synchronization.
Frame
U
S0
Frame
U
S0
S0
Master application task
Master application task
Master application task
Host controller
(master)
S0
Cycle time (1C32h: 02)
Shift time (1C33h: 03)
Calc and copy time
(1C33h: 06)
Inputs Latch
Cycle time (1C32h: 02)
Cycle time (1C32h: 02)
Shift time (1C32h: 03)
Outputs Valid
Sync0
event
Sync0
event
Slave
Network
Master user
shift time
Sync0 shift time
Calc and copy time
(1C32h: 06)
Sync0
event
U
Frame
