Siemens S7-1500PLC Key knowledge: Communication principle “illustrated”

2022-05-03 0 By

Siemens S7-1500PLC is used in medium and large projects, which is the upgraded version of S7-300/400PLC. Compared with 200/200 SMART PLC, 1500 is a little more difficult. Communication is a more important part, which has involved advanced applications.Serial communication and Parallel Communication Serial communication and parallel communication are two different data transmission methods.(2) single-ended and differential (3) simplex, duplex, not half duplex: This is a term used in communications to describe the direction of data transmission.1) Simplex: This communication mode provides one-way transmission of index data. It is used for data output and does not support a business to exchange data.2) Full Simplex: Data can be sent and received at the same time.Usually two pairs of twisted-pair cables are required to connect, and the communication line cost is high.Such as: RS – 422.3) Half Simplex, such as RS-485, most commonly used two, RS-485 pin three, OSI reference model At the heart of the communication network is the OSI (Open System Interconnection) reference model.In 1984, the International Organization for Standardization (ISO) proposed a seven-layer model of open system interconnection.OSI model is divided into physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer from bottom to top.(1) The Physical Layer defines the transmission medium, connector, and signal generator, and specifies the electrical and mechanical properties of the Physical connection, such as voltage, transmission rate, and transmission distance.Typical physical layer devices are hubs and Repeaters.With the physical layer, you can communicate with another computer over a wire.(2) Data Link Layer: determine the physical address of the transmission site and transfer the message to the protocol stack, and provide sequence control and Data flow control.Typical devices at the data link layer include switches and Bridges.A MAC address belongs to the data link layer and is equivalent to an ID card.With this layer, the bitstream that is being sent can be detected so that there is no error message.(3) Network Layer: Defines the IP-Internet Protocol (IP) logical address between devices to transmit data, connect devices in different broadcast domains, commonly used to organize routing.A typical network-layer device is a router.An IP address is an IP protocol that allocates a qun address to every network and every host on the Internet, shielding physical differences.With the IP address, the computer can access the Internet.The IP address is divided into two parts. The first three numbers represent the network and the last number represents the host.For example, in 192.168.0.1, 192.168.0 indicates the network and 1 indicates the host.The IP address can be changed as required.(4) Transport Layer: establish session connections, allocate service access points, and allow reliable or unreliable data transmission.Can provide communication quality testing services.The gateway is the most complex device in the Internet. It is the device at the transport layer and above.The data to be sent (big data) for subcontracting encapsulation, packet by packet sent, called the transmission layer.TCP and UDP are at the transport layer.TCP is used to send large amounts of data, subcontract to send, not received retransmission.UDP is used to send small amounts of data.