Datasheet
Table Of Contents
- Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
- 1.0 Introduction
- 2.0 Pin Description and Configuration
- 3.0 Functional Description
- 3.1 Transceiver
- 3.2 Auto-negotiation
- 3.3 HP Auto-MDIX Support
- 3.4 MAC Interface
- 3.5 Serial Management Interface (SMI)
- 3.6 Interrupt Management
- 3.7 Configuration Straps
- 3.8 Miscellaneous Functions
- 3.9 Application Diagrams
- 4.0 Register Descriptions
- 4.1 Register Nomenclature
- 4.2 Control and Status Registers
- TABLE 4-2: SMI Register Map
- 4.2.1 Basic Control Register
- 4.2.2 Basic Status Register
- 4.2.3 PHY Identifier 1 Register
- 4.2.4 PHY Identifier 2 Register
- 4.2.5 Auto Negotiation Advertisement Register
- 4.2.6 Auto Negotiation Link Partner Ability Register
- 4.2.7 Auto Negotiation Expansion Register
- 4.2.8 Mode Control/Status Register
- 4.2.9 Special Modes Register
- 4.2.10 Symbol Error Counter Register
- 4.2.11 Special Control/Status Indications Register
- 4.2.12 Interrupt Source Flag Register
- 4.2.13 Interrupt Mask Register
- 4.2.14 PHY Special Control/Status Register
- 5.0 Operational Characteristics
- 6.0 Package Information
- 7.0 Application Notes
- Appendix A: Data Sheet Revision History
- The Microchip Web Site
- Customer Change Notification Service
- Customer Support
- Product Identification System
- Worldwide Sales and Service
2016 Microchip Technology Inc. DS00002165B-page 35
LAN8720A/LAN8720AI
3.8.8.2 Far Loopback
Far loopback is a special test mode for MDI (analog) loopback as indicated by the blue arrows in Figure 3-11. The far
loopback mode is enabled by setting the FARLOOPBACK bit of the Mode Control/Status Register to “1”. In this mode,
data that is received from the li
nk partner on the MDI is looped back out to the link partner. The digital interface signals
on the local MAC interface are isolated.
FIGURE 3-13: FAR LOOPBACK BLOCK DIAGRAM
Far-end system
SMSC
Ethernet Transceiver
10/100
Ethernet
MAC
CAT-5
XFMR
Digital
RXD
TXD
Analog
RX
TX
Link
Partner
X
X
3.8.8.3 Connector Loopback
The device maintains reliable transmission over very short cables, and can be tested in a connector loopback as shown
in Figure 3-11. An RJ45 loopback cable can be used to route the transmit signals an the output of the transformer back
to the receiver inputs, and this loopback will work at both 10 and 100.
FIGURE 3-14: CONNECTOR LOOPBACK BLOCK DIAGRAM
SMSC
Ethernet Transceiver
10/100
Ethernet
MAC
XFMR
Digital
RXD
TXD
Analog
RX
TX
1
2
3
4
5
6
7
8
RJ45 Loopback Cable.
Created by connecting pin 1 to pin 3
and connecting pin 2 to pin 6.
3.9 Application Diagrams
This section provides typical application diagrams for the following:
• Simplified System Level Application Diagram
• Power Supply Diagram (1.2V Supplied by Internal Regulator)
• Power Supply Diagram (1.2V Supplied by External Source)
• Twisted-Pair Interface Diagram (Single Power Supply)
• Twisted-Pair Interface Diagram (Dual Power Supplies)