Datasheet

KSZ8081MNX/RNB
DS00002202A-page 26  2016 Microchip Technology Inc.
3.8 Loopback Mode
The KSZ8081MNX/RNB supports the following loopback operations to verify analog and/or digital data paths.
• Local (digital) loopback
• Remote (analog) loopback
3.8.1 LOCAL (DIGITAL) LOOPBACK
This loopback mode checks the MII/RMII transmit and receive data paths between the KSZ8081MNX/RNB and the
external MAC, and is supported for both speeds (10 Mbps/100 Mbps) at full-duplex.
The loopback data path is shown in Figure 3-8.
1. The MII/RMII MAC transmits frames to the KSZ8081MNX/RNB.
2. Frames are wrapped around inside the KSZ8081MNX/RNB.
3. The KSZ8081MNX/RNB transmits frames back to the MII/RMII MAC.
4. Except the frames back to the RMII MAC, the transmit frames also go out from the copper port.
FIGURE 3-8: LOCAL (DIGITAL) LOOPBACK
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.
MII/RMII
MAC
MII/
RMII
AFE
(ANALOG)
KSZ8081MNX/RNB
PCS
(DIGITAL)