Datasheet
2016-2018 Microchip Technology Inc. DS00002202C-page 27
KSZ8081MNX/RNB
The following programming action and register settings are used for local loopback mode.
For 10 Mbps/100 Mbps loopback,
•Set Register 0h,
Bit [14] = 1 // Enable local loopback mode
Bit [13] = 0/1 // Select 10 Mbps/100 Mbps speed
Bit [12] = 0 // Disable auto-negotiation
Bit [8] = 1 // Select full-duplex mode
The following steps should be applied if unwanted frames appear outside the copper port in the local feedback.
1. Set register 1Fh bit [3] to ‘1’ to disable the transmitter.
2. Run local loopback test as above.
3. Set register 1Fh bit [3] to ‘0’ to enable the transmitter.
3.8.2 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 3-9.
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 3-9: REMOTE (ANALOG) LOOPBACK
The following programming steps and register settings are used for remote loopback mode.
1. Set Register 0h,
Bits [13] = 1 // Select 100 Mbps 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
RJ-45
RJ-45
CAT-5
(UTP)
KSZ8081MNX/RNB
100BASE-TX
LINK PARTNER
AFE
(ANALOG)
PCS
(DIGITAL)
MII/
RMII