BECKHOFF EtherCAT IP Core for Altera FPGAs v3.0.10 - Manual (Page 72)

IP Core Signals
III-60 Slave Controller – IP Core for Altera FPGAs
8.1.1 Clock source example schematics
The EtherCAT IP Core and the Ethernet PHYs have to share the same clock source. The initial
accuracy of the EtherCAT IP clock source has to be 25ppm or better.
Typically, the clock inputs of the EtherCAT IP Core (CLK25, CLK100, and optionally CLK50 or
CLK25_2NS) are sourced by a PLL inside the FPGA. The PLL has to use a configuration which
guarantees a fixed phase relation between clock input and clock outputs, in order to enable TX shift
compensation for the MII TX signals.
CLK25
EtherCAT IP Core
Ethernet
PHY
MII
CLK25
PLL
CLK_IN CLK25
CLK100 CLK100
Ethernet
PHY
MII
CLK25
25 MHz
Ethernet
PHY
MII
CLK25
FPGA
Figure 20: EtherCAT IP Core clock source (MII)
CLK25
EtherCAT IP Core Ethernet
PHY
RMII
REF_CLK
PLL
CLK_IN CLK25
CLK100 CLK100
Ethernet
PHY
RMII
REF_CLK
50 MHz
CLK50 CLK50
FPGA
Figure 21: EtherCAT IP Core clock source (RMII)
CLK25
EtherCAT IP Core
Ethernet
PHY
RGMII
REF_CLK
PLL
CLK_IN CLK25
CLK100 CLK100
Ethernet
PHY
RGMII
REF_CLK
25 MHz
Ethernet
PHY
RGMII
REF_CLK
FPGA
REF_CLK
CLK25_2NS CLK25_2NS
Figure 22: EtherCAT IP Core clock source (RGMII)