The ENC28J60 is a stand-alone Ethernet controller with an industry standard Serial Peripheral Interface （SPI）。 It is designed to serve as an Ethernet network interface for any controller equipped with SPI. The ENC28J60 meets all of the IEEE 802.3 specifications. It incorporates a number of packet filtering schemes to limit incoming packets. It also provides an internal DMA module for fast data throughput and hardware assisted checksum calculation， which is used in various network protocols. Communication with the host controller is implemented via an interrupt pin and the SPI， with clock rates of up to 20 MHz. Two dedicated pins are used for LED link and network activity indication. A simple block diagram of the ENC28J60 is shown in Figure 1-1. A typical application circuit using the device is shown in Figure 1-2. With the ENC28J60， two pulse transformers and a few passive components are all that are required to connect a microcontroller to an Ethernet network. The ENC28J60 consists of seven major functional blocks： 1. An SPI interface that serves as a communication channel between the host controller and the ENC28J60. 2. Control registers which are used to control and monitor the ENC28J60. 3. A dual port RAM buffer for received and transmitted data packets. 4. An arbiter to control the access to the RAM buffer when requests are made from DMA， transmit and receive blocks. 5. The bus interface that interprets data and commands received via the SPI interface. 6. The MAC （Medium Access Control） module that implements IEEE 802.3 compliant MAC logic. 7. The PHY （Physical Layer） module that encodes and decodes the analog data that is present on the twisted-pair interface. The device also contains other support blocks， such as the oscillator， on-chip voltage regulator， level translators to provide 5V tolerant I/Os and system control logic.