Datasheet

Micrel, Inc.
KSZ8081MNX/KSZ8081RNB
August
19, 2015 33
Revision 1.4
Remote (Analog) Loopback
This loopback mode checks the line (differential pairs, transformer, RJ-45 connector, Ethernet cable) transmit and receive
data paths between the KSZ8081MNX/RNB and its link partner, and is supported for 100Base-TX full-duplex mode only.
The loopback data path is shown in Figure 9.
1. The Fast Ethernet (100Base-TX) PHY link partner transmits frames to the KSZ8081MNX/RNB.
2. Frames are wrapped around inside the KSZ8081MNX/RNB.
3. The KSZ8081MNX/RNB transmits frames back to the Fast Ethernet (100Base-TX) PHY link partner.
Figure 9. Remote (Analog) Loopback
The following programming steps and register settings are used for remote loopback mode.
1. Set Register 0h,
Bits [13] = 1 // Select 100Mbps speed
Bit [12] = 0 // Disable auto-negotiation
Bit [8] = 1 // Select full-duplex mode
or just auto-negotiate and link up at 100Base-TX full-duplex mode with the link partner.
2. Set Register 1Fh,
Bit [2] = 1 // Enable remote loopback mode