BECKHOFF EtherCAT Technology Section I - Manual (Page 34)

Frame Processing
I-14 Slave Controller – Technology
3.2 Frame Processing Order
The frame processing order of EtherCAT Slave Controllers depends on the number of ports (logical
port numbers are used):
Table 9: Frame Processing Order
Number of Ports Frame processing order
1 0→EtherCAT Processing Unit→0
2 0 →EtherCAT Processing Unit→1 / 1→0
3 0 →EtherCAT Processing Unit→1 / 1→2 / 2→0 (log. ports 0,1, and 2)
or
0
→EtherCAT Processing Unit→3 / 3→1 / 1→0 (log. ports 0,1, and 3)
4 0 →EtherCAT Processing Unit→3 / 3→1 / 1→2 / 2→0
The direction through an ESC including the EtherCAT Processing Unit is called “processing” direction,
other directions without passing the EtherCAT Process
ing Unit are called “forwarding” direction.
Ports which are not implemented behave similar to closed ports, the frame is forwarded to the next
port.
Figure 5 shows the frame processing in general:
1
Port 2
Auto-
Forwarder
Port 1
A
u
to
-
F
o
rw
a
rd
e
r
1
Port 3
Auto-
Forwarder
Port 0
A
u
to
-
F
o
rw
a
rd
e
r
Loopback function
L
o
o
p
b
a
c
k
f
u
n
c
ti
o
n
EtherCAT
Processing Unit
Loopback function
L
o
o
p
b
a
c
k
f
u
n
c
ti
o
n
EtherCAT
Slave Controller
port 2 closed
port 2 open
p
o
rt
1
c
lo
s
e
d
p
o
rt
1
o
p
e
n
port 3 open
port 3 closed
p
o
rt
0
o
p
e
n
o
r
a
ll
p
o
rt
s
c
lo
s
e
d
p
o
rt
0
c
lo
s
e
d
Figure 5: Frame Processing