1G/10Gbps Ethernet PHY IP Core can't work for 1Gbps rate transmission

Hello guys,

I encountered a problem that I can't use the 1G/10Gbps Ethernet PHY IP Core for 1Gbps rate transmission. I use loopback mode. When I set this core "SEQ Force Mode" register as 10GBASE-R, I can transmit and receive data correctly under 10Gbps rate. But when I set it as GigE, this core fail. From logic analyzer I found the signals have been sent to the input data port "gmii_tx_d", but I can't get any signals on output port "gmii_rx_d".

Does anyone run into the same problem? Please give me some clue or advice.

Thanks