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The composition of the Ethernet network board
According to the description of the CSMA/CD access method, the node network board has to perform a variety of tasks. Therefore, each network board must have its own control
The controller is used to determine when to send and when to receive data from the network, and is responsible for implementing the procedures specified in 802.3, such as forming a frame,
Calculate frame check sequence, perform codec conversion, etc.
1. LAN management part and microprocessor
The network circuit board (also called the network board, the network card or the network adapter) is composed of several parts, as shown in Figure 6.
Figure 6
The management part of the LAN is the core of the network board, responsible for executing all procedures and data processing. The microprocessor part includes the microprocessor core
chips, RAM chips and ROM chips. This part provides a link between the PC and the LAN management part. When the PC has data to send,
Interrupt the microprocessor part, store the data in the RAM chip of the microprocessor part, and command it to send data. The microprocessor will also
The signal from the PC is converted into a format acceptable to the LAN management part, and then the LAN management part is instructed to send the data to the network.
The microprocessor monitors the sending process and frequently visits the LAN management part to check whether the sending is successful.
Once the PC is ready to receive frames from the network, it interrupts the microprocessor and informs it that it can receive frames. Microprocessor communication
Instructed the LAN management part to start receiving frames in response. The microprocessor monitors the receiving process of the frame. Once received by the LAN
After the management part processing is over, the micro-organizer will interrupt the PC and transfer the received data to the PC.
It should be pointed out that some net boards do not contain a microprocessor part. In this case, the PC directly controls and monitors the LAN management part
work.
2. Manchester codec
IEEE802.3 or Ethernet stipulates that data transmission must be carried out with Manchester encoding. When the PC wants to send data to the network
When on the network, it is always transmitted byte by byte to the LAN management part in parallel, and the LAN management part is serially transmitted to "Non-return-to-zero (NRZ) Manchester"
特coder", Manchester coding is performed here. The coding process of Manchester is shown in Figure 7. NRZ Manchester coder receives
After arriving at the NRZ signal, it is encoded and then sent to the transmitter for transmission. When receiving Manchester code from the network, the receiver will
The process of passing it to the Manchester NRZ special converter and converting it back to NRZ signal is also called clock recovery. Therefore, very high accuracy is required.
The quality of LAN depends on the accuracy of clock recovery.
Figure 7
3. Sending and sending control part
The transmission and reception control part is responsible for the transmission of frames. It can be seen from Figure 6 that the sending part accepts the conversion from "NRZ Manchester
器" Manchester code data, and send the data to the media under the conditions allowed by the transmission control part, the transmitted data is called
TxD.
The transmission control part determines whether to send, and this determination is made based on the management part and TxD based on the LAN.
4. Receiving and receiving control part
The receiving and receiving control part is responsible for the frame reception. This part generates the signal whether there is a carrier in the network, and the basis for generation
is obtained from RxD. Therefore, the signal from the network is fed to the receiver on the one hand, and fed to the receiving control part on the other hand.
The receiving control part determines whether to operate the receiver according to the signal received on the LAN management part and the media. |
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China
Post time: 2020-8-7 22:00:01
