Datasheet
Table Of Contents
- 1.0 Introduction
- 2.0 Pin Description and Configuration
- 3.0 Functional Description
- 3.1 10BASE-T/100BASE-TX Transceiver
- 3.2 RMII Interface
- 3.3 Back-to-Back Mode – 100 Mbps Copper Repeater
- 3.4 MII Management (MIIM) Interface
- 3.5 Interrupt (INTRP)
- 3.6 HP Auto MDI/MDI-X
- 3.7 Loopback Mode
- 3.8 LinkMD® Cable Diagnostic
- 3.9 NAND Tree Support
- 3.10 Power Management
- 3.11 Reference Circuit for Power and Ground Connections
- 3.12 Typical Current/Power Consumption
- 4.0 Register Descriptions
- 5.0 Operational Characteristics
- 6.0 Electrical Characteristics
- 7.0 Timing Diagrams
- 8.0 Reset Circuit
- 9.0 Reference Circuits — LED Strap-In Pins
- 10.0 Reference Clock - Connection and Selection
- 11.0 Magnetic - Connection and Selection
- 12.0 Package Outline

2016 Microchip Technology Inc. DS00002199A-page 19
KSZ8081RNA/RND
3.7 Loopback Mode
The KSZ8081RNA/RND supports the following loopback operations to verify analog and/or digital data paths.
• Local (digital) loopback
• Remote (analog) loopback
3.7.1 LOCAL (DIGITAL) LOOPBACK
This loopback mode checks the RMII transmit and receive data paths between the KSZ8081RNA/RND and the external
MAC, and is supported for both speeds (10/100 Mbps) at full-duplex.
The loopback data path is shown in Figure 3-7.
1. The RMII MAC transmits frames to the KSZ8081RNA/RND.
2. Frames are wrapped around inside the KSZ8081RNA/RND.
3. The KSZ8081RNA/RND transmits frames back to the RMII MAC.
4. Except the frames back to the RMII MAC, the transmit frames also go out from the copper port.
FIGURE 3-6: TYPICAL CROSSOVER CABLE CONNECTION
FIGURE 3-7: LOCAL (DIGITAL) LOOPBACK
RECEIVE PAIR RECEIVE PAIR
TRANSMIT PAIR
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
TRANSMIT PAIR
10/100 ETHERNET
MEDIA DEPENDENT INTERFACE
10/100 ETHERNET
MEDIA DEPENDENT INTERFACE
MODULAR CONNECTOR
(RJ-45)
HUB
(REPEATER OR SWITCH)
CROSSOVER
CABLE
MODULAR CONNECTOR
(RJ-45)
HUB
(REPEATER OR SWITCH)
RMII
MAC
RMII
PCS
(DIGITAL)
AFE
(ANALOG)
KSZ8081RNA/RND