Interfacing Embedded Ethernet with ARM Cortex-M3 Processor-Based Controller LPC1768

1. Understanding the LPC1768 Ethernet Module

The LPC1768 ARM Cortex-M3 microcontroller Ethernet module includes an Ethernet MAC (Media Access Controller) that enables reliable embedded Ethernet communication for networking applications.

• Supports 10/100 Mbps operation
• Compatible with IEEE 802.3
• Supports MII (Media Independent Interface) and RMII (Reduced MII)
• Built-in DMA support for faster embedded Ethernet data transfer
• Hardware checksum generation for TCP/IP
• Supports Wake-on-LAN

To complete ARM Ethernet communication, the MAC requires an external PHY chip. Popular PHY chips used with the LPC1768 microcontroller Ethernet interface include:

• DP83848 (most common)
• KSZ8081
• LAN8720 (RMII mode)

2. Important Hardware Requirements

To interface embedded Ethernet with ARM Cortex-M3 LPC1768, the following hardware components are required:

Required Components

• LPC1768 ARM Cortex-M3 Ethernet development board
• Ethernet PHY chip (e.g., DP83848)
• RJ45 Ethernet connector with magnetic isolation
• 25 MHz crystal for PHY (based on PHY requirement)
• Ethernet isolation transformer
• Termination resistors and capacitors
• Ethernet cable (LAN cable)
• Power supply (3.3V)

Key Ethernet Pins on LPC1768

Depending on MII or RMII mode, the ARM Cortex Ethernet LPC1768 uses different pins.

RMII Common Pins

• TXD0, TXD1 – Transmit data
• TXEN – Transmit enable
• RXD0, RXD1 – Receive data
• CRS_DV – Carrier sense
• REFCLK (50 MHz) – PHY clock
• MDIO / MDC – PHY management interface

Ethernet requires a 50 MHz reference clock for reliable embedded Ethernet microcontroller operation.

3. Understanding MII vs RMII Interface

Before interfacing ARM Ethernet, you must choose between MII and RMII.

MII (Media Independent Interface)

• Uses 16 data pins
• Slower data rate on pins
• More complex routing
• Suitable for older microcontroller Ethernet designs

RMII (Reduced Media Independent Interface)

• Uses only 7 data pins
• Reduces PCB complexity
• Faster and more commonly used in embedded Ethernet ARM Cortex systems

Most modern LPC1768 development boards use RMII mode due to reduced pin count and simpler ARM Cortex Ethernet hardware design.

4. Configuring the Hardware Connections

Step 1: Connect LPC1768 to PHY

Connect the RMII signals from the ARM Cortex-M3 Ethernet microcontroller LPC1768 to the PHY chip.

Step 2: Connect PHY to RJ45 Connector

The PHY connects to the RJ45 jack through an Ethernet magnetic transformer, ensuring safe and standards-compliant embedded Ethernet communication.

Step 3: Power and Ground Connections

Both LPC1768 and PHY operate at 3.3V for microcontroller Ethernet operation.

Step 4: Clock Configuration

Correct clock configuration is critical for stable ARM Ethernet communication.

5. Configuring Ethernet Pins in LPC1768

The LPC1768’s ARM Cortex Ethernet pins are part of the PINSEL multiplexer and must be configured before initializing embedded Ethernet.

6. Initializing the Ethernet MAC

The following steps initialize the ARM Cortex-M3 embedded Ethernet MAC:

• Power on the MAC
• Reset the MAC
• Configure speed, duplex, and flow control
• Assign a unique MAC address
• Set up DMA descriptors

Once initialized, the microcontroller Ethernet MAC can transmit and receive Ethernet frames.

7. Initializing and Communicating with the PHY

The LPC1768 ARM Ethernet MAC communicates with the PHY using MDIO/MDC for embedded Ethernet control and status monitoring.

8. Integrating a TCP/IP Stack

For embedded Ethernet ARM Cortex communication, a TCP/IP stack is required.

• lwIP
• uIP
• Keil RTX TCP/IP
• FreeRTOS + TCP

lwIP is widely used for embedded Ethernet microcontrollers due to its lightweight design.

9. Testing Ethernet Communication

Testing confirms reliable ARM Ethernet communication:

• Ping test
• TCP server
• UDP client
• HTTP server

10. Applications of Ethernet on LPC1768

• Industrial automation controllers using embedded Ethernet
• Remote monitoring systems
• IoT gateways based on ARM Cortex Ethernet
• Web-based device configuration
• Data loggers
• Smart home controllers
• SCADA systems using microcontroller Ethernet