Analog Loopback uses the echoed signals from the unterminated MDI and decodes these signals in the Hybrid to return the data to the MAC.

Enable Loopback

Write register 0x0016 = 0x0108

Enable data generator/checker for MAC side

Write register 0x0619 = 0x1555

Write register 0x0624 = 0x55BF

Check incoming data from MAC side

Data can also be checked internally by reading registers 0x063C, 0x063D, 0x063E

Enable data generator/checker for Cable side

Write register 0x0619 = 0x0557

Write register 0x0624 = 0x55BF

Check data for Cable side

1. Write register 0x0620[1] = 1'b1
2. Read register 0x620
   1. Bit [7:0] = Number of errors bytes received
   2. Bit [8] = PRBS checker lock status on incoming data (1'b1 indicates lock)

Repeat steps 1 and 2 to continously check error status of incoming data stream.

Other system requirements

Data generate by the internal PRBS will be transmitted over the MDI and the MAC interface.