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2016-2017 Microchip Technology Inc. DS00002117F-page 25
KSZ9031RNX
3.13 Loopback Mode
The KSZ9031RNX supports the following loopback operations to verify analog and/or digital data paths.
• Local (digital) loopback
• Remote (analog) loopback
3.13.1 LOCAL (DIGITAL) LOOPBACK
This loopback mode checks the RGMII transmit and receive data paths between KSZ9031RNX and external MAC, and
is supported for all three speeds (10/100/1000 Mbps) at full-duplex.
The loopback data path is shown in Figure 3-5.
1. RGMII MAC transmits frames to KSZ9031RNX.
2. Frames are wrapped around inside KSZ9031RNX.
3. KSZ9031RNX transmits frames back to RGMII MAC.
FIGURE 3-5: LOCAL (DIGITAL) LOOPBACK
The following programming steps and register settings are used for local loopback mode.
For 1000 Mbps loopback,
1. Set Register 0h,
- Bit [14] = 1 // Enable local loopback mode
- Bits [6, 13] = 10 // Select 1000 Mbps speed
- Bit [12] = 0 // Disable auto-negotiation
- Bit [8] = 1 // Select full-duplex mode
2. Set Register 9h,
- Bit [12] = 1 // Enable master-slave manual configuration
- Bit [11] = 0 // Select slave configuration (required for loopback mode)
For 10/100 Mbps loopback,
1. Set Register 0h,
- Bit [14] = 1 // Enable local loopback mode
- Bits [6, 13] = 00 / 01 // Select 10 Mbps/100 Mbps speed
- Bit [12] = 0 // Disable auto-negotiation
- Bit [8] = 1 // Select full-duplex mode
3.13.2 REMOTE (ANALOG) LOOPBACK
This loopback mode checks the line (differential pairs, transformer, RJ-45 connector, Ethernet cable) transmit and
receive data paths between KSZ9031RNX and its link partner, and is supported for 1000BASE-T full-duplex mode only.
The loopback data path is shown in Figure 3-6.
1. The Gigabit PHY link partner transmits frames to KSZ9031RNX.
2. Frames are wrapped around inside KSZ9031RNX.
3. KSZ9031RNX transmits frames back to the Gigabit PHY link partner.