The article mainly introduces an Ethernet interface circuit design scheme based on Samsung ARM9 chip S3C2440 embedded system, and adopts industrial grade Ethernet controller DM9000AEP to successfully realize embedded system network data exchange. Based on the network interface circuit, the paper analyzes the driver and registry items of the Windows CE system control software part DM9000AEP.
With the development of microelectronics technology and computer technology, embedded technology has been widely developed and has become the development direction of modern industrial control, communication and consumer products. Ethernet has excellent performance in real-time operation, reliable transmission, standard unification, etc. It is easy to install and maintain, and is not restricted by communication distance. It has been widely concerned by many researchers in the field of monitoring and control at home and abroad. The application shows a significant advantage. This paper proposes a design scheme based on DM9000AE network interface chip and 32-bit Samsung ARM9 processor S3C2440 embedded system Ethernet interface, and develops network driver to realize network access on Windows CE operating system.
2. Working principle of DM9000AE
2.1 Main characteristics and overall structure of the DM9000
The DM9000AE is a 10/100M Fast Ethernet control chip developed by DEVICOM (Taiwan Lianjie International). DM9000AE implements Ethernet media medium access layer (MAC) and physical layer (PHY) functions, including MAC data frame assembly/split and transmit and receive, address recognition, CRC encoding/checking, MLT-3 encoder, and receive noise suppression. , output pulse shaping, timeout retransmission, link integrity test, signal polarity detection and correction. The internal logic structure of DM9000AE is shown in Figure 1.
DM9000AE has the following main features: 148-pin LQFP package, small pin size; 2 support 8/16-bit data bus; 3 for 10Base-T and 100Base-T, 10/100M adaptive, adapt to different network speeds Requirements, 4 built-in 16KB SRAM, used for sending and receiving buffers, reducing the speed requirements for the main processor; 5 support IP / TCP / UDP acceleration, reducing the CPU burden, improve network speed; 6 support Back pressure half-duplex flow control, Compatible with IEEE802.3u, supports IEEE802.3x full-duplex flow control; 720ns response time, 2.5V/3.3V low power consumption.
Figure 1 DM9000AE internal logic structure
2.2 Working principle
The DM9000AE can be connected to the microprocessor in an 8-bit or 16-bit bus and can be operated in simplex or full-duplex mode as needed. When the system is powered on, the processor configures the DM9000AE internal network control register (NCR), interrupt register (ISR), etc. through the bus to complete the initialization of the DM9000AE. Then the DM9000A enters the data transceiver waiting state.
When the processor wants to send data frames to the Ethernet, it first packs the data into UDP or IP data packets, and sends them to the data transmission buffer of the DM9000A byte by byte through the 8-bit or 16-bit bus, and then fills in the information such as the data length. In the corresponding register of the DM9000AE, the enable command is then sent, and the DM9000AE performs MAC grouping on the buffered data and data frame information, and sends it out.
When the DM9000AE receives the Ethernet data sent by the external network, it first checks the legality of the data frame. If the frame header flag is incorrect or there is a CRC check error, the frame data is discarded. Otherwise, the data frame is buffered to the internal RAM. And the processor is notified by the interrupt flag bit, and the processor processes the data of the DM9000AE receiving RAM after receiving the interrupt.
The DM9000AE automatically detects the network connection and sets the internal data transmission and reception rate to 10 Mb/s or 100 Mb/s according to the network speed. At the same time, the DM9000AE can also change the direction of the data transceiver pin according to the RJ45 interface connection mode. Therefore, the system can communicate normally regardless of whether the external network cable is in the same or cross mode.
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