A current loop communication system for two-wire half-duplex multi-computer communication

Abstract

The invention discloses a current loop communication method and system based on two-wire system half-duplex one-master multi-slave multi-machine communication. According to the method, a current direction gating switch is designed on a master station by utilizing two communication lines; a light-emitting diode of a receiving optical coupler of each slave station is reversely connected in parallel with a phototriode of a sending optical coupler of the slave station; and two current loops with the opposite directions are realized between the master station and the slave station, and are used for transmitting data from the master station to the slave station and from the slave station to the master station. According to the current loop communication method and system, the loading capacity of current loop communication is increased; a data sending and receiving direction control port is provided; the data can be transparently transmitted without complicated program logic control; the current loop communication has the characteristics of good anti-jamming property, long communication distance, a great number of slave stations, low network topology requirement and low cost; and a current loop communication port can replace an RS485 bus to serve as a communication interface for acquiring data of various instruments and instrument equipment.

Description

technical field [0001] The invention relates to the technical field of serial communication, in particular to the occasion where the RS485 interface is used to collect equipment data such as instruments and instruments. Background technique [0002] In the occasions that need to collect data in instruments, meters and other equipment, the RS485 interface is mostly used, but it has several problems. First, the construction requirements are high, and the network topology must be a hand-in-hand bus type; second, the communication line should be shielded Or use shielded twisted pair; third, the anti-interference is poor, in order to avoid the interference of strong electricity, the 485 bus should avoid running together with strong electricity; fourth, the impact of failure is large, and a single node failure will cause the bus to be paralyzed. [0003] Current loop communication has the advantages of good anti-interference, long transmission distance, and low requirements for wi...

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Problems solved by technology

[0002] In the occasions that need to collect data in instruments, meters and other equipment, the RS485 interface is mostly used, but it has several problems. First, the construction requirements are high, and the network topology must be a hand-in-hand bus type; second, the communication line should be shielded Or use shielded twisted pair; third, the anti-interference is poor, in order to avoid the interference of strong electricity, the 485 bus should avoid going together with strong electricity; fourth, the impact of failure is large, and a single node failure will cause the bus to be paralyzed

[0003] Current loop communication has the advantages of good anti-interference, long transmission distance, and low requirements for wires and network topology. However, there are still some problems in the current current loop circuit. One-to-one communication can be realized, and the circuit is complicated when multi-machine communication

There are also two communication lines, and the receiving and sending optocouplers of the master station are connected in series with the receiving and sending optocouplers of the slave stations to form a current loop on the communication lines. There are two problems in this method. One is that the receiving and sending optocouplers of the master station The optocoupler is connected in series in the current loop, receiving the forward conduction current I of the optocoupler LED F And phototransistor collector current I C Restrictions, the number of slave stations that can be accessed is limited, mostly within 10; second, the receiving and sending optocouplers of the master station or slave station cannot independently complete the receiving and sending of data, and it is necessary to program the relevant logic of the microprocessor to Ensure the normal operation of the current loop

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