1000BASE-X auto-negotiation is described in IEEE Std 802.3, clause 37. This function allows a device to advertise the supported modes of operation to a device at the remote end of a link segment (the link partner on Ethernet), and detect corresponding operational modes advertised by the link partner. The results of the auto-negotiation can be read from the 1000BASE-X Management Auto-Negotiation Link Partner Ability Base register (Table 7). The speed should be set to 1G and Duplex bit to Full duplex.
There are two methods that can be used for the completion of an auto-negotiation cycle:
- By polling the auto-negotiation complete bit of 1000BASE-X Management Status register (Register 1, bit 5, Table 3).
- By using the auto-negotiation complete interrupt ( and 1000BASE-X Management Auto-Negotiation Interrupt Control register, Table 12).
When placed into loopback, data is routed from the transmitter to the receiver path at the last possible point in the PCS/PMA sublayer. This is immediately before the transceiver interface. When placed into loopback, a constant stream of Idle code groups is transmitted through the transceiver. Loopback in this position allows test frames to be looped back within the system without allowing them to be received by the link partner. The transmission of Idles allows the link partner to remain in synchronization so that no fault is reported. Loopback can be enabled or disabled by writing to the 1000BASE-X Management Control register bit 14 (Table 2).