SNLS614A September 2018 – December 2018 DP83869HM
The DP83869HM supports the 1000Base-X Fiber Ethernet protocol as defined in IEEE 802.3 standard. In 1000M Fiber mode, the PHY will use two differential channels for communication. In fiber mode, the speed is not decided through auto-negotiation. Both sides of the link must be configured to the same operating speed. The PHY can be configured to operate in 1000BASE-X through the register settings (Register Configuration for Operational Modes) or strap settings (Strap for DP83869HM Functional Mode Selection).
In 1000Base-X Fiber applications, a MAC will often read the link status of the PHY before initiating data transfer. In rare cases, MAC intervention is required to ensure 1000Base-X link up. It is recommended to use the application note DP83869 1000Base-X Link Detection(SNLA305) for identifying 1000Base-X link. This approach is not needed in 100BASE-FX mode.