There are several options for loopback tests that test and verify various functional blocks within the PHY. Enabling loopback mode allows you to inspect the connections between the MAC and the PHY using xMII/PCS/Digital/AFE loopbacks as well as between the PHY and the MDI using reverse loopback.

Figure 2-22 MAC-Side Analog Loopback Mode Example

Figure 2-23 Block Diagram, Reverse (Cable-Side) Loopback Mode

The analog loopback is recommended for checking the full data path between the MAC and PHY, while reverse loopback is used with a link partner to verify the data path between the PHY and the MDI(Link Partner).

The device also incorporates an internal PRBS Built-in Self Test (BIST) circuit to accommodate in-circuit testing or diagnostics. BIST can be performed using various loopback modes to isolate any issues to specific parts of the data path by generating packetized data with variable content. Scripts are provided to enable data generator and checker as well as the various loopback modes.

Figure 2-24 Data Generator and Checker With Loopback