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
LAN8720A/LAN8720AI
DS00002165B-page 22 2016 Microchip Technology Inc.
The internal logic of the device detects the TX and RX pins of the connecting device. Since the RX and TX line pairs
are interchangeable, special PCB design considerations are needed to accommodate the symmetrical magnetics and
termination of an Auto-MDIX design.
The Auto-MDIX function can be disabled via the AMDIXCTRL bit in the Special Control/Status Indications Register.
FIGURE 3-4: DIRECT CABLE CONNECTION VS. CROSS-OVER CABLE CONNECTION
1
2
3
4
5
6
7
8
TXP
TXN
RXP
Not Used
Not Used
RXN
Not Used
Not Used
1
2
3
4
5
6
7
8
TXP
TXN
RXP
Not Used
Not Used
RXN
Not Used
Not Used
Direct Connect Cable
RJ-45 8-pin straight-through
for 10BASE-T/100BASE-TX
signaling
1
2
3
4
5
6
7
8
TXP
TXN
RXP
Not Used
Not Used
RXN
Not Used
Not Used
1
2
3
4
5
6
7
8
TXP
TXN
RXP
Not Used
Not Used
RXN
Not Used
Not Used
Cross-Over Cable
RJ-45 8-pin cross-over for
10BASE-T/100BASE-TX
signaling
3.4 MAC Interface
3.4.1 RMII
The device supports the low pin count Reduced Media Independent Interface (RMII) intended for use between Ethernet
transceivers and switch ASICs. Under IEEE 802.3, an MII comprised of 16 pins for data and control is defined. In devices
incorporating many MACs or transceiver interfaces such as switches, the number of pins can add significant cost as the
port counts increase. RMII reduces this pin count while retaining a management interface (MDIO/MDC) that is identical
to MII.
The RMII interface has the following characteristics:
• It is capable of supporting 10Mbps and 100Mbps data rates
• A single clock reference is used for both transmit and receive
• It provides independent 2-bit (di-bit) wide transmit and receive data paths
• It uses LVCMOS signal levels, compatible with common digital CMOS ASIC processes
The RMII includes the following interface signals (1 optional):
• transmit data - TXD[1:0]
• transmit strobe - TXEN
• receive data - RXD[1:0]
• receive error - RXER (Optional)
• carrier sense - CRS_DV
• Reference Clock - (RMII references usually define this signal as REF_CLK)